Phenom II with the 5850 would be better, as most games arent CPU limited the bottleneck tends to fall to the GPU which is where the 5850 would give the phenom II the advantage. Even when it is a CPU bottleneck, on both of those CPUs your bottleneck will be well above the playable thresh hold so it wont matter.
You can run any game on the highest detail settings with a 5770, expect for maybe crysis at 1080p. If you game at 720p though you can easily run every game with a 4850. I'd say the bottom-end for PC gaming would be cards weaker than the 4850.
5850 is the way to go. The 5770 struggles to play games that are out right now at smooth fps at 1900x1200 res. It can't even play dirt2 super smooth at 1900x1200 res, which uses dx11. Some people like to crossfire te 5770 to get great performance for the $, but some games still don't recognize two graphics cards.