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:
The 560 Ti (900 Mhz) gets a total of 862 fps in those games to the 590's 881. The twin 560's costs you $440 or $0.67 per frame. The 590 costs you $700 or $0.79 per frame. And lately, when available, the 590 is up to $750.