the 5870 and 6950 1gb perform better than 560Ti on many benchmarks and scaling just makes the 560Ti look ridiculous. not much difference between the 5870 and 6950 other than HD3D. price difference between 5870 and 6950?
5870 is a good card and if the savings are really worth it (like you could buy 2 for just a little more than a single 560/6950) then it's a great one to buy.
The 5870 is often quite similar in performance to 6950 and 560Ti, but unfortunately in some cases it falls way behind. I would say get the cheaper of the 560 or 6950. They perform extremely close to eachother.