Following thread on teksyndicate forum has tweaks, and explaining;
enjoy.

Feel free to ask any question on forum.

https://forum.teksyndicate.com/t/witcher-3-tips-tricks-performance/80663



Content of thread:
=====================
=====================



First of all, this is not about any downgrade but to improve performance&visuals through out the game.
(those are my own settings, and my own opinion)

@UPDATE 1.04
Every time you upgrade all those tweaks are removed with default settings.

Always make backups before editing files.

=======================
First place owners of Nvidia GPU's have to look at (amd owners of 7970, 8970, 280x, 270x, 285 can edit present)
The Witcher 3 Wild Hunt\bin\config\performance.xml

Edit file with notepad or similar one.
Find your GPU
1) Remove 'fpslimit="30'.
2) Edit preset="X" and change X to "3" this will allow for higher quality textures, draw distance etc.
=========================
=========================
\The Witcher 3 Wild Hunt\bin\config\base\resources.ini

FileQueueSizeGame = 250
FileQueueSizeLoading = 700
MaxRequests = 45 [50 is max, and with 50 or over you might have crashes]

(bigger faster loading)
MaxCompressedBudget = 10

MaxUncmpressedBudget = 240
MaxUncompressedBlocks = 4096
==============================

How to improve performance of hairworks overall in AMD GPU's (not that i personally feel like there's need)
(this will also decrease quality and amount of hair)

Inside your AMD Catalyst Control Center
Gaming > Create custom game profile, or use default (up to you)

Look for Tasselation options "Maxiumum Tasselation" and lower it. (2x is lowest, 16x is a middle ground, 32x looks good, and is pretty much same as 64x)
==============================

Warning this will fork it out further beyond ultra.

\The Witcher 3 Wild Hunt\bin\config\base\rendering.ini

AllowMSAA=false [keep false, doesn't work]

MaxTextureSize=3048
MaxAtlasTextureSize=3048
MaxCubeShadowSize=1024
MaxSpotShadowSize=1024

TextureMemoryBudget=1500
TextureMemoryGUIBudget=180
TextureInFlightBudget=128

TextureStreamingDistanceLimit=440000.f
TextureStreamingReduceGameplayLOD=true

UberSampling=0 [keep at 0 or 1 = disabled, doesn't work at the moment]

DynamicDecalsLimit=60
MeshRenderingDistanceScale=4.0f
MeshLODDistanceScale=0.0f
TerrainScreenSpaceErrorThreshold=1.6f
TerrainErrorMetricMultiplier=6

GlobalOceanTesselationFactor=64
UseDynamicWaterSimulation=true
UseHairWorks=true
HairWorksAALevel=8 [lower this if you have decreased hardware performance in hairworks]
TerrainReadAheadDistance=600.0f

MeshLodGameplayDownscale=0
CharacterLodGameplayDownscale=0
DecalsHideDistance=100
StripeHideDistance=120
SwarmHideDistance=400
DimmerHideDistance=260

DecalBudget=200
=========================

\The Witcher 3 Wild Hunt\bin\config\base\visuals.ini

[will take longer to load if your gpu isn't fast enough]
MovieFramerate=60.0
=========================

After change of this file I recommend making it read-only as full screen mode is buggy sometimes and it will switch to borderless, this way you don't have to come back and change settings again -> each time you update you need to make writable again...

C:\Users[username]\Documents\The Witcher 3\user.settings

VSync=false
FullScreenMode=2 [many people will have 1 = borderless, this decreases performance dramatically]
VSyncThreshold=0

SpawnedLimit=200

cvMaxAllowedLightsShadowTime=3
cvMaxAllowedGrass=60000
cvMaxAllowedDecalsDynamic=20
cvMaxAllowedDynMeshes=107857600
cvMaxAllowedChunksSkinnedTime=3.5
cvMaxAllowedTrianglesSkinned=100000

cvMaxAllowedLightsShadow=5
cvMaxAllowedActiveEnvProbesTime=0.3
cvMaxAllowedStatTextures=514572800
cvMaxAllowedSpeedTree=5000
cvMaxAllowedLightsNonShadowsTime=0.2
cvMaxAllowedChunksStatic=1500
cvMaxAllowedTrianglesStatic=500000
cvMaxAllowedHiresChunks=25
cvMaxAllowedDecalsDynamicTime=0.5
cvMaxAllowedLightsNonShadows=40
cvMaxAllowedChunksStaticTime=1.5
cvMaxAllowedChunksSkinned=400
cvMaxAllowedApexDestroTicked=40
cvMaxAllowedStatMeshes=409715200

cvMaxAllowedHiresChunksTime=0.2
cvMaxAllowedApexTickedTime=0.5
cvMaxAllowedCharTextures=209715200
cvMaxAllowedParticlesCountTime=0.2
cvMaxAllowedParticlesCount=2000
cvMaxAllowedGrassTime=1.5

OcclusionQueryAdditionalMemory=20
cvMaxAllowedDecalsSS=160

GrassDensity=3400
DecalsSpawnDistanceCutoff=20
TextureStreamingHeadsDistanceLimit=20
GlobalOceanTesselationFactor=128
TextureStreamingCharacterDistanceLimit=70
CascadeShadowFadeTreshold=1
CascadeShadowDistanceScale2=1.5
TextureStreamingDistanceLimit=60000
MaxCascadeCount=4
TextureMemoryBudget=2400
CascadeShadowDistanceScale3=1.5
MeshLODDistanceScale=0
ScaleformTextureUnstreamDelay=2.5
DecalsChance=1
TerrainReadAheadDistance=600
HairWorksLevel=2
TerrainScreenSpaceErrorThreshold=1.6
MaxTerrainShadowAtlasCount=4
TextureInFlightCountBudget=12
TerrainErrorMetricMultiplier=4
CascadeShadowmapSize=3072
CascadeShadowDistanceScale0=1
MeshRenderingDistanceScale=1
CascadeShadowQuality=1
CascadeShadowDistanceScale1=1

UseDynamicWaterSimulation=true

LimitFPS=0

GrassGenerationEfficiency=0.075
GrassDistanceScale=1
FoliageDistanceScale=1
FoliageShadowDistanceScale=64
GrassRingSize=16777216

MaxVisibilityDepth=24
===========================

You can find additional possible var that could be specified inside config files here:
[Do not change those files - unless you know what you are doing.]
\The Witcher 3 Wild Hunt\bin\config\r4game\user_config_matrix\pc

Feel free to ask question about settings, I or someone else on the forum might be able to explain what do they do.

Here are links to pastebin for my own configs (note thay are little bit different from those settings, but feel free to use them)

\The Witcher 3 Wild Hunt\bin\config\base

resources.ini
http://pastebin.com/sAN6a3mR3

rendering.ini
http://pastebin.com/xRSTeBx92

\The Witcher 3 Wild Hunt\bin\config
performance.xml
http://pastebin.com/NT1Cy6F54

Nice! But what if I only want to get best fps performance? :)

performance drop between full screen & borderless is quiet significant on my end & the game keeps launching as borderless after restart. Make sure to run the game at full screen mode.
I'm also noticing performance drop after alt+tab, its better to save & quit the game rather than alt+tabbing.

What if your GPU isn't listed in that file? I have GTX 680 and it's not listed as an option in the performance.xml file.

@shishimaru1000
Depends on your hardware, and what graphical fidelity you want.

@Beligerent
Doesn't matter, most likely its defined together with one of listed ones.