I know they are more powerful. I had a 5770 before, not impressed. I was more impressed with the performance from the GTX 460 (and to some extent the 450)
I have owned the 430, 450, 460 and 470 (which was a great card) with my core i3, then upgraded to a core i5
Everything (bar the 430) now sold as waiting for Intel to release motherboards for Sandy Bridge-EN socket R 2011, so I can build myself an 8 core (16 with hyper threading) system and quad channel memory.
This will also be PCIe v3.0, up to 20mb cache and memory bandwidth more than double that of socket 1155