there is a known problem with Geforce cards due to inefficient texture management.
the management portion that handles Texture Eviction is not functioning, normal games are also getting these issues.
im using 92.91 myself since any newer had way to many issues to bother with (all of which were caused by the broken clockrates and overclocking panel...)
anyhow. the problem is that Textures fill up the vram and spill of into the system apperture which is MUCH slower then the vram, and the only way to fix this is to either force a buffer flush by either Alt-tabbing to the desktop, or Alt-entering to reenlarge the screen
this problem effects
Geforce 6
Geforce 7
Geforce 8
there are also problems with the way Geforce 8 cards report to games, as where a game expects and attempts to cache to a 1gb card, it instead caches 768mb to the card and 256mb to system memory..... again, a fix is expected soon.