GTX 560 ti 1GB model. Or for your budget gtx 560. CAn run that game pretty great on those cards i just mentioned. You should be fine. AS far as AMD. I would go with 5870's crossfire. That seems to be a common build for most people purchasing previous series GPU's. Dont have alot of expierence with it so dont quote me on it. Maybe 6670's crossfire (not sure about that either sorry just trying to help). Two 5670's may cut it call amd?
No liability accepted or warranty given for advice