Welcome to the forums.
the GTX 560Ti is comparable with HD 6950 not the HD 5870, so a GTX 560Ti is a little better than HD 5870.
here's a comparison between the HD 5870 and GTX 560Ti, so HD 5870 is doing pretty good but the GTX 560Ti is awesome http://www.anandtech.com/bench/Product/294?vs=330
if you're going to play @ 1680 x 1050 you can grab the HD 5870 as it performs better than a HD 6870, the GTX 560Ti is a great implementation for DX11 and will let you max out any game at this resolution.
and if you're saying that HD 5870 is on par with HD 6950, check out each review and check out this http://www.anandtech.com/bench/Product/293?vs=294
Note : reviews above compares GTX 560TI as the reference design card, but if you compare the TWIN Frozer II to HD 5870, it's non comparable with it.
there's nothing really called Proof, but so far the GTX 560 Ti, HD 6950 are maxing out each game outside except for Metro 2033 and Crysis 2, those 2 games specially requires SLI to run great. and with some pure overclock to the twin frozer you'll get a really good performance out of this GPU.
and as i said above, if you're only playing at 16850x the HD 5870 will do the job just fine...no worries.
The 5870 scored 460 fps in Guru3D's gaming test suite
The 560 Ti scored 455 fps in Guru3D's gaming test suite
The 900 MHz 560 Ti scored 495 fps in Guru3D's gaming test suite
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.
Glad to this thread is still open 6950>560 ti
6950=5870 just so we are clear these reviews you posted are in fact reviews specific to the 560ti which these sites are endorsing.
But very odd how the 5870 really isn't shy that much 5-9 frames of the 570 in the review I posted but somehow in those reviews specific to the 560ti it seems to smash the card 5870.
I would rather have the 560 ti anyway but im sorry by posting reviews to a card someone is being paid to review isn't all that convincing