Hey guys, not sure if you all are aware of this, but it was posted on the official forums (i take no credit for it's discovery).
Pretty much everyone can relate to having their worst performance outdoors in the thick grass. Worst still, the thick grass means you can't even see where that wolf is that's attacking you. The simple solution would be to turn off grass, resulting in a HUGE performance increase (more so than turning off HDR), however, there is a much better solution.
By default Oblivion's grass is very thick. This means lots of sprites to render, and your graphics card struggling under the toll. However, this can be changed.
Go to your Oblivion game folder, then open the doc "OBlivion_default" in that directory.
Search for [Grass], to get to this section:
[Grass]
iMinGrassSize=80
fGrassEndDistance=3000.0000
fGrassStartFadeDistance=2000.0000
bGrassPointLighting=0
bDrawShaderGrass=1
iGrassDensityEvalSize=2
iMaxGrassTypesPerTexure=2
fWaveOffsetRange=1.7500
Ok, so by default, the iMinGrassSize (ie, the density of grass) is 80. The smaller this value, the MORE dense the grass is. What i recommend is increasing this to 120-200. You can now afford to make the Grass Fade and End distances obscenely high, like 5000.0000 and 10000.000 respectively, without taking a performance hit.
I set iMingrassSize=140, and i immediately noticed a great performance increase. Try it out, and do a bit of experimenting.
