I would definitely go no lower than a 650ti Boost and if its in your budget just go straight to the 660. I'm planning on getting the 670 2GB card when I upgrade my entire PC, but that'll be in january when I get 3 pays, plus holiday and more than likely my tax return as well.


As for the power supply I would use this PSU Calc to give you a general idea of how big of a PSU you will need