^ And what?
The ranks in performance are:
1. GTX 460
2. GTX 275
3. GTX 260
4. 9800 GTX
The best choice would be the GTX 460 which not only performs the fastest, but overclocks the best out of all those graphics cards should you need more performance. Also runs nice and cool, and does not use much power.
What is your CPU? Core i7 900 or i7 800? Regardless, reely is right - you should add more RAM.