GTX 260 or 9800GX2?
do you use on or 2 moniters?
one monitor only..... 9800gx2
2 monitors... GTX 260 (i would personally get the GTX 280 though)
From personal experience I have a GTX260 and it runs conciderably faster than the 8800GTX GTS's that I have had. Runs Nvidia Froggy fricken amazing fast.....
Truthfully the GTX260 will run any game perfectly.....Only reason I got the GTX260 over the 9800GTX2 was A.) the GTX260 is newer and B.) Heard some nightmares about heat issues with the GX2....Performance wise the 9800GTX2 might be a better performer in some games.
Start here for an idea of performance differences
Make sure you don't confuse the 9800 GTX and the 9800 GX2
Personally, I have a 9800 GX2 at home and a GTX 260 at work - and my 9800 GX2 is clearly faster for the games I play. I mostly play Grid and Crysis though and always at 1920x1200. Either way, both are fast enough to play just about anything out today.
I have the GTX260 and can play anything cranked @ 1920X1200. One thing that made me choose the nvidia over ati is heat generation and power consumption. My room is already hot enough and using less power is always a good thing.
Heat is probably the only thing keeping me from getting a 4870 X2 right now... Just can't have something idling in my box at over 70 C.