I can give you my experiences, without benchmarks to back it up.
e6400 @ 2.4GHz
2GB DDR2
Recently only been playing WoW.
x1900gt rev2 ran 1600x1200 + 4xAA smooth as silk with all eye candy on (everything pushed to limits)
7600GT would only run 1280x1024 under same settings
Note: 7600GT was purchased as a replacement card from the forums here when the x1900gt (Sapphire) started overheating and artifacting up badly (ten month old card, never overclocked). (Newegg honored their "standard return policy" very well and refunded 95% of my original purchase price, no complaints on their service at all!)