Well I didnt really dig up any benchmark scores but AFAIK 9800 series are not cards that is really the card for the money, they are more expensive and the performance difference is not that much compared to 8800 series, so a 8800 GT with 512 MB or a better 8800 GTS 512 would be a better choice... Today I saw the new cards for nvidia on gamespot, the 260 series or something like that, the prices are steep but the performance is much much better then the 9800 series, so the 9800 would get cheaper, but the bad thing is this new set of cards require like 550 W for power source, which means heating problems...
I have 2 gigs of ram, 8800 GTS OC and a dual core something and I play on ultra high, everything topped to the greatest detail and I am forcing AA, did no OC and the game works well... The thing is I dont play latest games much, since I still play Imperialism II, Chaos Gate and FM 08

so I dont pay for high end cards