I don't know how much more powerful than normal humans you want Astartes to be but here's some things to consider:

If your Gene-Seed is a boost applied to a single body part like the torso then it still allows other implants to be added and unbalance the Astartes or just makes them op to begin with.

For instance, a vanilla Jogger pawn has a move speed of 5-cells/sec, boosted by Archotech Legs and a Bionic Heart to 7.9, which drops to 4.45 after a total of 22 damage to the legs. Your Astartes with just Archotech Legs has a 16.7 ms, which only drops to 5.45 after one leg has been destroyed and the other has taken 25 damage. My idea of an Astartes has a 15.12 ms, which drops to 4.48 after one leg is destroyed and the other takes 11 damage. At 25 damage to their remaining leg they would become incapable of walking.

A vanilla pawn with Archotech Arms is reduced from a 165% to a 98% Surgery Success Chance by taking a total of 22 damage to the arms, while your Astartes with Arch Arms goes from a 352% to a 224% SSC even after losing an arm and taking 25 damage to the other. My Astartes would have a 220% SSC, which drops to 98% if they take 15 damage to each arm.

Therefore, I think it would be best if there were multiple implants that replace most of the body. Because there are only so many body parts that can be replaced, some gene-seed implants may need to be combined(I.E. Mucranoid and Melanochrome, Biscopea and Ossmodula) as adding new parts alters how likely each body part is to be hit. This also reduces how much Gene-Seed is necessary to make a full Astartes.

Also, the Torso, Pelvis, Head, Neck, Skull and Brain still act as if natural parts even when made bionic. Neck implants remove the entire head and all attached parts without killing the pawn who can move and act as if they still had a head.


All that said, this is my recommendation for Astartes implants:

Sus-an Membrane(Skull): 100% eff, Medical Potency +50%

Catalepsean Node(Brain): 100% efficiency, Rest Fall Factor 0.4x, Rest Rate Multiplier +40%, Hunger Rate 0.5x, Mental Break -34%

Occulobe(Eyes): 200% eff, 6.5 Shooting Accuracy

Lyman's Ear(Ears): 200% eff, 5 Melee Dodge Chance

Neuroglottis(Nose): 200% eff, Negotiation Ability +32%, Trade Price Improvement +34%, Social Impact +50%, Tame Animal Chance +33%, Train Animal Chance +36%, Toxic Sensitivity -10%

Betcher's Gland(Jaw): 200% eff, Eating +20%, 3.9 Range, 17 Damage, 40% Armor Penetration, 90% Touch Range Acc, 0.75-sec Warm-Up, 0.75-sec Cooldown, 1 'Round'

Melanocranoid(Torso): 100% eff, -16-C Comfy Temp Ming, +24-C Comfy Temp Max, Toxic Sensitivity -10%

Omophagea(Spine): 100% eff, Global Learn Factor +50%

The Maintainer(Heart): 200% eff, Natural Healing Factor 3x

Multi-Lung(Lungs): 200% eff, Toxic Sensitivity -10%

Preomnor(Stomach): 200% eff, Hunger Rate 0.33x, Toxic Sensitivity -15%, Food Poisoning Chance Factor 0x

Larraman's Organ(Liver): 200% eff, Rest Fall Factor 0.5x, Immunity Gain Speed +50%, Toxic Sensitivity -15%

Oolitic Kidney(Kidneys): 200% eff, Immunity Gain Speed +50%, Toxic Sensitivity -10

The Black Carapace(Sternum): 100% eff, Move Speed +1.5, Global Work Speed +40%

Biscodula(Ribcage): 100% eff, Carrying Capacity +50, Move Speed +0.5, Global Work Speed +10%, Incoming Damage Factor 0.5x

Astartes Arm(Shoulders): 200% eff, 30 Damage, 20% Armor Penetration, 1.5-sec Cooldown

Astartes Leg(Legs): 150% eff, Carrying Capacity +50, 2.5 Melee Dodge Chance, 40 Damage, 20% Armor Penetration, 2-sec Cooldown

An Astartes with the above balance can move, work, eat, heal and rest 3x faster than normal, has 6x carry capacity and immunity gain speed, takes half damage from all attacks and has 90% toxin resistance. They have a Mental Break Threshold of 1%, take about 6x longer to become Hungry and 5x longer to become Tired. They can withstand temperatures ranging from 0`C or 32`F(freezing) to 50`C or 122`F(RW animal max) without clothing, having higher ranged accuracy, melee damage and melee dodge chance and there are other bonuses like better taming/training/trading/social skills, etc. I didn't give any Pain or Bleed reductions because Bionics do not feel pain or bleed so only an Astartes' pelvis, skull, torso, neck, head and brain could feel pain and only the last four could bleed or scar.

Because the Tough Trait reduces damage taken by 50%, combined with Biscodula an Astartes would take only 25% damage. As this might be OP it may be best for the Biscodula to not give dmg resistance, which would make pawns with the Tough Trait the "only viable" candidates to become Astartes. Additionally, as the Iron-Willed Trait reduces Mental Break by -18% you may want the Catalepsean Node to only reduce it by -16% instead of -34% so that Tough and Iron-Willed pawns are among the most viable Astartes candidates, with the addition of Jogger being the perfect 3 mix.

I don't know how skilled you are at modding but if you created a Projenoid Gland implant for the pelvis it could generate Gene-Seed overtime that could be harvested to make more implants. I.E. In 40K lore it takes 5 years for the first Proj Gland to mature, which may be too long in RW but each Proj Gland in the colony reduces the time it takes to generate GS. If limbs don't cost GS to make then at a rate of 1 every 12 days you could get 20 GS every 4-years to make a full Astartes, while 4 Proj Glands in the colony would increase that to 1 Astartes/year. Prisoners/Slaves/Servitors could be used to harvest GS.


A vanilla RW Human with the Jogger Trait has a Move Speed of 5-cells/sec, increased to 7.5 with Go-Juice.
An Astartes Jogger with the above balance has a MS of 15.12, increased to 18.62 with GJ.

If Power Armor reduces MS by 1 then the Human has a MS of 4, increased to 6 with GJ.
In PA the Astartes moves at 12.96, increased to 15.96 with GJ.

If Term Armor reduces MS by 2 then the Human has a MS of 3, increased to 4.5 with GJ.
In TA the Astartes moves at 10.8, increased to 13.3 with GJ.

If Heavy weapons like the Hvy Bolter reduce MS by 0.5 then the Human has a MS of 4.5/ 3.5 in PA/ 2.5 in TA, increased to 6.75/ 5.25/ 3.75 with GJ.
With Hvy wpn the Astartes moves at 14.04/ 11.88/ 9.72, increased to 17.29/ 14.63/ 11.97 with GJ.

If Super Hvy wpns like the Assault/Plasma Cannon reduce MS by 1 then the Human has a MS of 4/ 3/ 2, increased to 6/ 4.5/ 3 with GJ.
With Spr Hvy wpn the Astartes moves at 12.96/ 10.8/ 8.64, increased to 15.96/ 13.3/ 10.64 with GJ.

A Human Jogger with Archotech Legs, a Bionic Heart and GJ moves at 10.4, the safest top speed possible in vanilla RW, which an Astartes could slightly surpass even in TA with an Assault Cannon if they were on GJ.


Rimworld's Armor system is set up so that each powered armor takes an average of about 25% less Assault Rifle, 20% less Charge Rifle and 17% less Charge Lance damage than the armor below it when compared to similar quality weapons.
I.E.
Legendary Cataphract takes less damage than Leg Marine does from Leg weapons.
Leg Mar takes less damage from Leg weapons than Mastercraft Cat does from Mast weapons.

Normally, Armor Rating is capped so Leg Cat is only 200 instead of 216. If Armor Rating is uncapped then Leg Cat would take about 76% less AR, 41% less CR and 33% less CL damage than Leg Mar causing it to become rather OP against vanilla weapons; however, it also allows for an additional armor tier to be added above it.

138 for Terminator, which is equal to Good Cata
120 for Power Armor, which is equal to Norm Cata
106 for Scout/Carapace, which is equal to Norm Mar
92 for Kevlar Armor, which is equal to Norm Recon
80 for Flak Armor, which is twice vanilla Flak Armor

Realistically speaking, Flak Armor should be a 6+ Save with Kevlar/Ballistic/Combat Armor as the 5+. That said, it's safe to assume Imperial tech would be superior to most others', which is why their Flak deflects a bit less than 1/3rd of Assault Rifle shots instead of a bit less than 1/8th like vanilla Flak.

Depending on weapon(Assault Rifle, Charge Rifle, Charge Lance) and quality(Normal to Legendary), RW full Flak takes about 25% less torso and 150% more limb damage than Recon Armor does, while taking about the same torso and 275% more limb damage than Marine Armor does. A Flak Vest with a Hyperweave Duster takes about the same torso and 180% more limb damage than Cataphract does.

If Imperial Flak and Kevlar are just a middle layer they can be worn with a Flak Vest/Jacket or Duster or Imperial equivalents such as a Great Coat. The Imp Flak with RW Flak or equiv would take similar full body but more head damage than Recon against lower AP weapons, while with a Hyperweave Duster or equiv would take similar full body but more head damage than Marine against lower AP weapons. Imp Kevlar would take more head damage than Marine but with RW Flak or equiv would take similar full body damage and with Duster or equiv would take slightly less full body damage against lower AP weapons.


If each point of Armor Penetration is 20% then AP6 is 25% higher than an Assault Rifle, Bolter AP5(40) sits between the Charge Rifle(35) and Charge Lance(45) and the Heavy Bolter AP4(60) has 34% more AP than the Charge Lance. AP- weapons like the Auto/Lasgun should be made AP6 so they aren't outclassed by vanilla weapons against Armor Ratings of 200+.

With the above AP system, against Legendary Terminator Armor:
AP- and 6 are deflected 100% of the time.
AP5 is deflected 94% and mitigated 6% of the time.
AP4 is deflected 79% and mitigated 21% of the time.
AP3 is deflected 64% and mitigated 36% of the time.
AP2 is deflected and mitigated 49% of the time.
AP1 is deflected and mitigated 34% of the time.

Against Legendary Power Armor:
AP- is deflected 100% of the time.
AP6 is deflected 93% and mitigated 7% of the time.
AP5 is deflected 78% and mitigated 22% of the time.
AP4 is deflected 63% and mitigated 37% of the time.
AP3 is deflected and mitigated 48% of the time.
AP2 is deflected and mitigated 33% of the time.
AP1 is deflected and mitigated 18% of the time.


For damage I've been testing the following scale:
S1: 2 dmg
S2: 10 dmg
S3: 17 dmg
S4: 30 dmg
S5: 40 dmg
S6: 51 dmg
S7: 63 dmg
S8: 76 dmg
S9: 90 dmg
S10: 110 dmg

S3 weapons(I.E. Auto/Lasgun) do about 13.3% more damage per hit than the Charge Rifle. S4 weapons(I.E. Bolter, Astartes Arm punch) are able to destroy a pawn's limbs, organs and head with a single unmitigated hit, while S5 weapons(I.E. Heavy Bolter, Astartes Leg kick) can destroy any body part with a single unmitigated hit. If Astartes have either the Tough Trait or 50% dmg resistance their limbs and head would technically have 60-hp, which a S7 Plasma weapon could still one-shot if unmitigated.

S10 at Legendary quality reaches 165 dmg allowing it to one-shot a pawn's torso even if mitigated by armor twice. A once mitigated S10 could still one-shot an Astartes' torso, while a double mitigation would leave them with 50% hp. Even if the S10 attack was mitigated 3x by an Iron Halo, Combat/Storm Shield and Armor as well as reduced by Astartes Toughness it would still do enough damage to destroy the Astartes' brain if it hit.


A 20 Shooting Skill pawn has an accuracy value of 99%, which totals out to:
Close Range(3-tiles): 97%
Short Range(12-tiles): 89%
Medi Range(25-tiles): 78%
Long Range(40-tiles): 67%

The only way to increase those values are with increased eyesight that maxes at 200% or with +Shooting Accuracy, which requires 40-pts to max accuracy on its own. The +25% efficiency of Bionic Eyes is essentially +3 acc and Arch's +50% is +6 acc. Astartes Occulobes at 200% efficiency and +6.5 acc each would give the Astartes +25 acc in total, requiring only 15 more to max out. Carapace/Scout, Power and Term Helmets can be +5, while PA is +5 and TA is +10.

With Archotech Eyes, TA and helmet a 20 Shooting pawn's accuracy would be:
Close Range: 99%
Short Range: 98%
Medi Range: 95%
Long Range: 92%

Astartes base acc is:
Close Range: 99%
Short Range: 98%
Medi Range: 96%
Long Range: 93%

Astartes with TA and helm is max possible accuracy:
Close Range: 100%
Short Range: 99%
Medi Range: 98%
Long Range: 96%

Because the Careful Shooter Trait increases accuracy by 5 then it may be best for each Occulobe to only boost acc by +4; however, because the Aiming Time Increase/Decrease of Careful Shooter/Trigger Happy does not equally impact all weapons and can make some become more OP than others it may be best to disable those Traits when using a 40k mod.