Came across this. Currently using the high balanced setting since I've only got a 460 gtx, and my game is super smooth and I'm quite happy with overall quality of the scene.
The user.ini is located in the /Documents/Witcher2/Config folder. Make copy of the original setting in case if you want your original settings back.
The problem with the Witcher 2 custom user.ini's is twofold: first, the configurator is bugged so that it doesn't always set custom settings correctly, retaining old settings (like the max shadow size etc) or even forgetting to completely put in whole variables (it loves to leave the FoliageDistance variable out, which means your grass/foliage distance is at some unknown level.)
When editing your user.ini, it needs to have ALL of these variables in it. If your user.ini doesn't have these in it, you're not adjusting all of the settings!
Next, if you want to make sure the Configurator doesn't rape your custom made settings, you MUST right click on your user.ini, go to Properties, and set it to Read-Only. Otherwise the game will muck everything up.
Here's some of my suggested configs for different PC's: Medium/High (Performance Focused), High Settings with Balanced IQ/Performance, and Ultra+ for those of you who max out Ultra and want more detail.
Feel free to play with MeshDistanceScale and FoliageDistanceScale to acquire your ideal image quality/performance balance on object LOD and foliage LOD/pop-in.
Med-High Settings
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[Rendering]
TextureDownscale=0
AtlasTextureDownscale=0
DetailTextureDownscale=0
MaxTextureSize=1024
MaxAtlasTextureSize=2048
TextureMemoryBudget=500
TextureTimeBudget=10
MaxCubeShadowSize=512
MaxCubeShadowCount=2
MaxSpotShadowSize=512
MaxSpotShadowCount=2
FoliageDistanceScale=0.9
MeshDistanceScale=0.9
CharacterLodGameplayDownscale=0
AllowBloom=0
AllowShafts=1
AllowAntialias=0
AllowBlur=0
AllowDOF=0
AllowDecals=1.0
AllowVignette=1
AllowSharpen=0
AllowRain=1
AllowSSAO=0
AllowMotionBlur=0
AllowScatterDOF=0
AllowCutsceneDOF=0
DanglesLimiter=0
ShadowQuality=2
ShadowedLights=2
Fullscreen=1
VSync=0
UberSampling=0
High Settings for Balanced Image Quality and Performance, 1 GB VRAM
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[Rendering]
TextureDownscale=0
AtlasTextureDownscale=0
DetailTextureDownscale=0
MaxTextureSize=2048
MaxAtlasTextureSize=4096
TextureMemoryBudget=650
TextureTimeBudget=10
MaxCubeShadowSize=1024
MaxCubeShadowCount=2
MaxSpotShadowSize=1024
MaxSpotShadowCount=2
FoliageDistanceScale=1.0
MeshDistanceScale=1.0
CharacterLodGameplayDownscale=0
AllowBloom=0
AllowShafts=1
AllowAntialias=0
AllowBlur=1
AllowDOF=0
AllowDecals=1.0
AllowVignette=1
AllowSharpen=0
AllowRain=1
AllowSSAO=0
AllowMotionBlur=0
AllowScatterDOF=0
AllowCutsceneDOF=0
DanglesLimiter=0
ShadowQuality=2
ShadowedLights=3
Fullscreen=1
VSync=0
UberSampling=0
Ultra Settings requiring at least 1.5g Vram
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[Rendering]
TextureDownscale=0
AtlasTextureDownscale=0
DetailTextureDownscale=0
MaxTextureSize=2048
MaxAtlasTextureSize=4096
TextureMemoryBudget=1000
TextureTimeBudget=10
MaxCubeShadowSize=2048
MaxCubeShadowCount=4
MaxSpotShadowSize=2048
MaxSpotShadowCount=4
FoliageDistanceScale=1.6
MeshDistanceScale=2.2
CharacterLodGameplayDownscale=0
AllowBloom=0
AllowShafts=1
AllowAntialias=1
AllowBlur=1
AllowDOF=1
AllowDecals=1.0
AllowVignette=1
AllowSharpen=1
AllowRain=1
AllowSSAO=1
AllowMotionBlur=1
AllowScatterDOF=1
AllowCutsceneDOF=0
DanglesLimiter=0
ShadowQuality=3
ShadowedLights=3
Fullscreen=1
VSync=0
UberSampling=0