I bought and installed Spec Ops a while ago on a Steam sale. I installed it and it looked great but I was getting terrible stuttering on transitions, loading enemies, etc... I looked into it a little at the time and I believe all i found(didn't look very hard) was adjusting the pool size in the SREngine.ini. Fast forward to current day and I decided to re-install and try again. After a little more searching I found the following steam post https://steamcommunity.com/app/268500/discussions/0/392183857621700482/

This worked like a freaking charm!
I feel like it wasn't specifically easy to find for someone looking to fix Spec Ops on Linux. So, I decided to post this here to create another search option for people in the future. Below is the important part...

Here they are: (REMEMBER, READ CAREFULLY, MATCH EXACTLY)
"*"=setting
"bUseTextureStreaming=True" (these are default for most but not all UE3 games)
"bUseBackgroundLevelStreaming=True"
"MipFadeInSpeed0=0" (these even out mipmap loads and draw time)
"MipFadeOutSpeed0=0"
"MipFadeInSpeed1=0"
"MipFadeOutSpeed1=0"
"PhysXGpuHeapSize=64" (these balance physx calls even on cpu based physx titles)
"PhysXMeshCacheSize=16"
"bSmoothFrameRate=TRUE" (this really does need to be on, ignore what you've read)
"MinSmoothedFrameRate=30" (keep these right here. setting higher/lower does no good)
"MaxSmoothedFrameRate=400"
"bInitializeShadersOnDemand=True" (reduces overall shader batch call size)
"DisableATITextureFilterOptimizationChecks=False" (driver based opt is MUCH faster)
"UseMinimalNVIDIADriverShaderOptimization=False" (same here)
"PoolSize=256" or (vidmem/poolsize exmpl: 512/128, 1024/256, etc, DO NOT exceed 768)
"bAllowMultiThreadedShaderCompile=True" (should already be on by default)
"ThreadedShaderCompileThreshold=4" (formulate like this: # of cpu-cores (not threads) -2)
"OnlyStreamInTextures=True" (reduces overall texture batch call size)

Check for multiple instances of these settings within this file as some games have them listed twice and you must change both (I.E Xcom:Enemy Unkown)

Now save the file, then right click it, choose properties and then set it to "read-only".
Launch your game, choose reset to defaults under that games graphics settings, then set them up how you want. These settings get saved to your profile file for that game and use the engine ini as a base. They are not saved to the ini file therefore it wont matter that it is read-only. However there are a few rare exceptions (SEE NOTE BELOW)

THAT'S IT.

Hopefully this might help someone in the future.

Also note that I achieved even better results by leaving VSync OFF & enabling "Force Composition Pipeline" & "Force Full Composition Pipeline" in Nvidia X Server Settings. After editing the SREngine.ini & using Force Composition Pipeline, any slowdowns that I had in the game seemed to behave purely on the hardware side(how it should be)

Anyone have other Unreal Engine games I could try this out on? Also, posting other Linux Unreal Engine games might help some other impatient soul fix his game!