this except in nvidia "tweaked" games (grrrr crysis)
On that note I'd mention that Blizzard loves optimizing for nvidia cards. (If I remember correctly they actually had a major content patch for WoW before Wrath that was dedicated in part to nvidia optimization...)
Granted for D3 and SC, either will do you more than well enough. Hell, a GTX 260 will handle either game like a champ too. If you're looking to save some cash up front I'd pick up a GTX 260, and when the 300 series cards come out pick up a second GTX 260 when the price drops and go SLI.
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