I have a Phenom II X4 940 along with an HD4890 (very close to a GTX 460 768mb) and I play SC2 at Ultra at 1920x1200 just fine. (1v1, 2v2, 4v4)
My cousin has a Phenom II X3 720 along with a GTX 460 768mb and he has no problem, but he is not playing as much as I am.
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