i use...

an Asus 7850, and I do just fine on ultra for campaign and high for multiplayer. Graphics cards definitely have a point of diminishing returns in terms of your money invested, where the difference between 400 and 300 is significantly less than the difference between 300 and 200. One other thing to consider might be that the new consoles are coming out soon, and it might be  a good idea to wait and see how new console games perform on current high end cards. Just some thoughts, hope they help.