Doom 3 is another game where the 320MB 8800GTS shows no penalty against its 640MB variant. The difference between the 320MB and 640MB GTS is minute but the faster core in the 320MB is paying off. Note also that the 7950GT shows some real value against even the 8800GTS. As for that slow start for the GTX XXX, we've seen this before. This would seem to be a factor of the GTX choosing not to use all of its 128 stream processors. It would rather save its steam for the higher resolutions.
Quake IV
The story QIV is also the same: the 320MB and 640MB are neck to neck even at the highest resolution, highest filter and quality settings. The 7950GT however falters at the highest resolution.