Define greatest .... fastest card ? ...... best bang fir the buck ? .... best reviewed ?
To my mind I agree with the reviewer here ..... never seen any card dominate like this one does:
http://www.techpowerup.com/reviews/ASUS/GeForce_GTX_670_Direct_Cu_II/33.html
Overall the ASUS GTX 670 Direct CU II is the best card I ever tested.
Now that covers the thread title......as far as the two you listed, here's how they shape up against the competition
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 (lowest price from major brand (Asus, Gigabyte, MSI, EVGA) in dollars per frame single card - CF or SLI:
$ 135.00 6850 (371/634) $ 0.36 - $ 0.43
$ 180.00 6870 (434/701) $ 0.41 - $ 0.51
$ 240.00 6950 (479/751) $ 0.50 - $ 0.64
$ 250.00 6950 Frozr OC (484/759) $ 0.52 - $ 0.66
$ 150.00 560 Ti (455/792) $ 0.33 - $ 0.38
$ 340.00 6970 (526/825) $ 0.65 - $ 0.82
$ 210.00 560 Ti - 900 Mhz (495/862) $ 0.42 - $ 0.49
So the 6870 is faster than the 6850 (434 - 371 fps) but the 6850 has a much better "bang for the buck" at $0.36 per frame ... only the 560 does better at $0.33 per frame and it outscores the 6870 (455 to 434)
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121446
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127592