Depends on how much you want the PhysX. A card that will run the game at maximum settings will cost you quite a bit. For high end cards I think the 670 seems to be your best bet. Or 680 if you have the extra money to spend. However, if your playing all the games you want at the settings you...
I just upgraded a week ago from an E7500 to a 3570k. The difference is light and day. But I like to play everything maxxed out at 1080. Oh yea and I had the e7500 overclocked to 4.06 GHz but it was still holding me back :(