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
But for now i'll stick with the core 2 duo