Today....the 6870 is the best "bang for the buck" card ya can get for under $200 at just $0.37 per frame.... I'd urge ya to stretch ya budget a bit )7.5%) more to $215. The 900 Mhz 560 Ti gives ya a 14% improvement over the 6870 in single card config but in SLI ($430) its 862 fps beats the ($450) 580' 616 fps by 40%, the ($480) 7950 603 fp by 43% and the $560 7970's 675 fps by 28%.
Guru3D uses the following games in their test suite, COD-MW, Bad Company 2, Dirt 2, Far Cry 2, Metro 2033, Dawn of Discovery, Crysis Warhead. Total fps (summing fps in each game @ 1920 x 1200) for the various options in parenthesis (single card / SL or CF) are tabulated below along with their cost in dollars per frame single card - CF or SLI:
And yes the factory overclocked version are different cards than the reference models w/ oversize coolers, beefed up PCB's with extra phases on the VRM's for extra overclock ability. But everything will start changing in a week or so as the 78xx and new keplers arrive.
I am hearing bad things about the Zotac cards so I don't know if it's worth paying 20 dollars less for something that will burn up shortly after purchase. I am a bit scared moving to ATI as it has been years since my last ATI card and I get a bit nervous as it was nothing but problems for me but clearly the 6870 seems to be the best price wise.
at this moment I agree with the 560ti. 6870 is also a good alternative if you need to spend a little less. Also this may be hear say, but since D3 is a major point for you I have heard Blizzard games work better with Nvidia cards. Not a fanboy remark (I own 2x 6950s in CFX) but it is something to look into.