First, the 560 Ti has it all over the 6850, especially of ya get one of the factory overclocked jobs with the robust VRM and better coolers.....they can generally be had e same price generally as the stock models.
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:
$ 155.00 6850 (371/634) $ 0.42 - $ 0.49
$ 215.00 560 Ti - 900 Mhz (495/862) $ 0.43 - $ 0.50
As you can see, the 6850, costs ya 42 cents per frame as a single card, penny less than the 560....but that's 124 fps more or 33% faster ..... jumps to 36 % faster in SLI.....but uncle not going there with his MoBo.
Ya can't judge PSU's by brand name..... 1st, 95% of the brands you know are built by someone else and while one product line might be great, another might be cruddy..... The Corsair HX850 gets 10.0 rating for example from jonnyguru but the HX1050 gets a more pedestrian 8.5
I'd suggest the XFX Core edition 650 ..... that's a 9.5 performance rated PSU by jonnyguru available for a mere $60 (after $30 MIR) ..... The GS600 is $25 more, TX650 $35 more. http://www.newegg.com/Product/Product.aspx?Item=N82E16817207014http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story9&reid=216