so the gtx 560 ti is obviously a better choice?
got that from the chart did you??
then look at it again...its slightly in favour of the amd card.
then ignore the line above
Basically these two cards perform at par...the 6950 edges ahead slightly on higher resolutions and it should because its a high end derivative.
Its only a matter of price you get and personal preference for amd or nvidia when choosing between the two.
Keep in mind though that the 6950 being more powerful naturally would draw more power and be a bit noisy than its nVidia counterpart.
Also the GTX560 Ti offers PhysX.
Hope all this helps you.