I believe you should compare best IQ possible for each card.
IE: 16x FSAA and 8xAF with NV35 and 6x FSAA and 16xAF with R350 32 FP and 24 FP. Run at 1024x768.
I would take the card that is faster. Either way IQ will look astounding.
I play at those settings on my R300 ALWAYS and yet I have seen a games minimum framerate EVER drop below 35fps at ANY time.
"Never before has any voice dared to utter the words of that tongue in Imladris, Mr. Anderson" - Elrond LOTR