Avoid ATI 7970 - are nice card, but not for CloD, with "final Patch" they stuck with the "magic dashed square" graphical bug and flicker a lot (sim faults). Probable same with 7950, since ATI 69xx dont have problem.
http://i48.tinypic.com/1z1wg2q.jpg
I would buy a GTX570, but read the "recommended settings with 1gb, 2 gb card" thread an choose 7970...
Sokol1