I was also confused between phenom and fx but i purchased FX 4100 and currently using it right now with AMD Radeon 6850 without overclocking. I can play Battlefield 3, NFS The run and other games in ultra settings without any problem.
My specs are:
CPU: AMD FX 4100
GPU: AMD Radeon 6850
I think, AMD FX are not that bad. at least for me.
I was running similar, Same Card, more memory and 6850 and play Battlefield 3 also without issues.
its a good chip that's deffo worth looking at.