Best ultra settings graphics card for a 1280x1024 40'' monitor

Hello, Everybody
I'm looking to max out bf3, skyrim etc. and i'm not sure what card i should pick, currently i have a 9800 gts and its faulty so i dont trust nvidia. Im thinking my new build will be an amd system because my 9800 build is intel/nvidia and my core 2 duo is still running like new so i completely trust intel. My resolution is low but it looks like 1980x1200 on such a big screen plus i have a 21 inch laptop screen thats full 1080p 1920x1280 and i cant tell the difference other than the size on the two screens. I cant afford the next gen of "keplar" and "tahiti" cards because they are like $500 per. And im looking to go cheap as possible with as much power as possible $500-$800 is my budget. If i get a cheaper X4 amd cpu will i bottleneck a higher end gpu like a 6850?
advice would be appreciated.