Which Graphic Card I Choose

Solution
Get any core 2 quad processor any one can handle the hd7850. You can get a powerful processor like core 2 quad q8400 and go with more powerful gpu like hd 7970

Xttony

Distinguished
Go for the AMD HD7850 1GB graphics card. This graphics card will probably be bottlenecked by the CPU but you can lower the clock settings manually. Or you can just go with a HD7770 or a GTX 650 without any bottlenecks