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:
$ 160.00 6870 (434/701) $ 0.37 - $ 0.46
$ 215.00 560 Ti - 900 Mhz (495/862) $ 0.43 - $ 0.50
$ 450.00 580 (616/953) $ 0.73 - $ 0.94
$ 480.00 7950 (603/NG) $ 0.80 - ERR
$ 560.00 7970 (675/NG) $ 0.83 - ERR
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.