In vanilla, the system is very shallow. You have three options:
- Small thrusters (1x1x2)
- Large thrusters (2x3x4)
- Gravity drive (1^3*x+1^3*y)

Ignoring the latter for hopefully apparent reasons, we're left with only two tiers of thrust. Neither are sufficient for even cruiser class ships.

You however have brought to us some relief:
- Small thrusters (1x1x2)
-- MKII variant (1x1x2)
-- MKIII variant (1x1x2)
-- MKIV variant (1x1x2)
- Large thrusters (2x3x4)
-- MKII variant (2x3x4)
-- MKIII variant (2x3x4)
-- MKIV variant (2x3x4)

This is well and good, but lacks some of the finesse brought by filling the gap between large and small.

The Proposal: Bridge the gap of power and size between large and small thrusters with variants of medium thrusters and giving situational thruster bonuses where applicable.

I am specifically looking to the addition of (2x2x3) medium grade thrusters with your variants added. Additionally to expand the proposal and tiers to give players a true feeling of tier^3 is to have slightly more specialized thrusters. We can't exactly play with this too much but we already have some options. Primarily thrust, power consumption, and thruster damage.

What we can do with this is give players the situational choice between Economy thrusters, Normal thrusters, and Overdrive thrusters.

So what's the difference?

An Econ Thruster offers cleaner more efficient power. A lesser power draw, thrust, thruster DMG range and efficient part cost(more power then average for number of parts used). What does that mean for the average player? Fine tuned drones on the lowest tiers and at the highest a very nice 'bang for your buck' on cruiser class. Rejoice you tree hugging Yankees!
- Reduced Power usage: 45% of 'Normal'
- Reduced Thruster power: 60% of 'Normal'
- Reduced Thruster DMG range: 50% of 'Normal'
- Reduced Thruster cost: 50% of 'Normal'

An Overdrive Thruster offers dirty and raw power. Higher power draw, thrust, thruster DMG range, and expensive part cost. This means players can now have high performance fighters and battle ships which feel like cruisers. Where's your god now hippie dude?
- Increased Power usage: 180% of 'Normal'
- Increased Thruster power: 175% of 'Normal'
- Increased Thruster DMG range: 160% of 'Normal'
- Increased Thruster cost: 190% of 'Normal'

Notes: In order to supplement some of what is proposed here, existing tiers may need to be reformatted. An example is T1 Normal small thrusters would now need to be made more expensive to accommodate T1 Economy small thrusters. This is a tentative recommendation as many people are familiar with the existing thrusters and the cost associated with them.