Copy everything:

Film grain amount = 0 (The game's "movie" filter, i dislike it)

AA = off (BIG PERFORMANCE IMPACT)

Filtering Mode = Bilinear, Trilinear or x16 (small performance impact)

Vsync = OFF (caps your framerate to 60) (adds latency)

The reason for shader detail being medium is the water being transparent which could give you an advantage here's what it looks like in death toll chapter 2
(BIG PERFORMANCE IMPACT ABOVE MEDIUM)

Shader: LOW

Shader: MEDIUM

Effects: MEDIUM or above so you can see tanks rocks from afar. (medium performance impact)

Texture: LOW (small performance impact)

Go on Library > Right-click Left 4 Dead 2 > Properties

-heapsize 750000 -high -novid -nojoy -nosteamcontroller +mat_motion_blur_percent_of_screen_max 0 +motion_blur_enabled 0

-console - enables dev console
-high - high priority in windows
-novid - no intro
-nojoy - no controller checking
-nosteamcontroller - no steam controller checking
+mat_motion_blur - removes motion blur
-noborder - borderless windowed mode
-windowed / -fullscreen
-heapsize 750000 - less lag and crashes with mods that reach the game's 256 mb mem limit, increases it to 512mb

copy an existing .cfg file rename it to autoexec and paste the commands below

// EcoDoBoteco's L4D2 CFG. use // to disable a setting or set to default value.

sv_cheats 0
con_enable 1

// FPS cap // default 300, cap to your monitor's refresh rate (60, 144, 240hz)
//fps_max "101"
cl_showfps 1

// Viewmodel
//cl_viewmodelfovsurvivor "58" // default "51", values = 60, 65, 70, 80, 90, 180 (no viewmodel)

// Sensibilidade
//sensitivity "1.3"

// Crosshair
//cl_colorblind "1"
//cl_observercrosshair "1"
//cl_crosshair_thickness "1"
//cl_crosshair_dynamic "1"
//cl_crosshair_alpha "255"
//cl_crosshair_blue "255"
//cl_crosshair_green "255"
//cl_crosshair_red "255"

// Chat
voice_enable "1"
voice_modenable "1"
cl_showtextmsg "1"

// Net settings
cl_updaterate "100" // default 20; common values: 30, 60, 100
cl_cmdrate "100" // default 30; common values: 30, 60, 100
rate "786432" // default 10000; 131072 = 1 mbps 786432 = 6 mbps max
cl_resend "1.5" // default 6; How many seconds to wait before retrying to connect to a server
cl_timeout "60" // default 30
cl_interp_ratio "0" // default 2; Improves hit registration, lerp settings
cl_interp "0" // default 0.1; Improves hit registration, lerp settings
// common values 0, 0.0167, 0.033, 0.067
cl_lagcompensation "1" // default 1; Improves hit registration
cl_pred_optimize 2
cl_downloadfilter nosounds // custom server content download
net_maxcleartime 0;net_maxfilesize 64;net_maxroutable 1260;net_maxfragments 1260
cl_allowdownload 1;cl_allowupload 1
cl_smooth 1;cl_smoothtime .1

// Audio
//volume 0.33
//snd_musicvolume 0.33
dsp_enhance_stereo "1" // 0 = low/medium 1 = high
dsp_slow_cpu "0" // 1 = low 0 = medium/high
// Sound buffering. (try it with 0.01 then increase till your sound stops lagging, default is 0.1)
snd_mixahead "0.066"
snd_disable_mixer_duck 0
snd_pitchquality 1
snd_spatialize_roundrobin 0
dsp_room 1
dsp_speaker 50
dsp_water 14
dsp_spatial 40
snd_defer_trace 0

// Loading
cl_forcepreload "1" // default 0; Pre-load levels entirely into RAM (only use if you have 2GB of RAM or more) reduces in-game stuttering, but makes you wait longer to join servers.
sv_consistency "0" // for mods
sv_pure_kick_clients "0" // for mods
cl_disablehtmlmotd 1

// graphic settings
mat_grain_scale_override "0.0" // film / grain filter
cl_ragdoll_limit 0 // ragdoll limit
r_flex 1
r_teeth 1
r_eyes 1
r_eyemove 1

// Survivor & Infected Glows
cl_glow_survivor_health_bleed_pulse "1" // bleed pulses of the survivor
cl_glow_survivor_health_bleed_pulse_amount "1" // intensity of pulsations when bleeding out 0-1 def 0.3
cl_glow_survivor_health_bleed_pulse_speed "10" // Heart rate when bleeding a person survivor 0-100 def 10
cl_glow_survivor_health_include_buffer "1" // Include a temporary health buffer when displaying health of the survivors.

// Null-cancelling movement
bind w +mfwd
bind s +mback
bind a +mleft
bind d +mright
alias +mfwd "-back;+forward;alias checkfwd +forward;"
alias +mback "-forward;+back;alias checkback +back;"
alias +mleft "-moveright;+moveleft;alias checkleft +moveleft;"
alias +mright "-moveleft;+moveright;alias checkright +moveright;"
alias -mfwd "-forward;checkback;alias checkfwd none;"
alias -mback "-back;checkfwd;alias checkback none;"
alias -mleft "-moveleft;checkright;alias checkleft none;"
alias -mright "-moveright;checkleft;alias checkright none;"
alias checkfwd none
alias checkback none
alias checkleft none
alias checkright none
alias none ""

// Fixed Third Person
Bind "F8" "thirdpersonshoulder"
c_thirdpersonshoulderoffset "0"
c_thirdpersonshoulderaimdist "720"
c_thirdpersonshoulderdist "40"
c_thirdpersonshoulderheight "5"
cam_ideallag "0"

//Fim
echo ECODOBOTECO CONFIG LOADED!

After all these tweaks does the game still run like ♥♥♥♥?

Try a few of the performance enhancing mods on the workshop, check out this collection by me

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3501393271