^Theoretically 7850 should be much better than 560 Ti but NVIDIA's gamble paid off: The similar core cluster configuration in the GTS 450/GTX 550/GTX 460/560 series gives developers a very rich base to optimize for: Make your code work well with one of these GPUs and all four families will benefit from it. This is a hard benefit for any developer to ignore.
For this reason all these GPUs will (eventually) gain the upper hand over their respective competitors (when it comes to price vs. performance, power notwithstanding), until a more popular GPU family replaces them (currently GTX 460/560 is the most popular DX11 GPU as per Steam hardware survey).