I'm running an i5 760 @ 3.8 - 4.2 GHz (I change it often) and two HD6900-series GPU, and I'm in no way bottlenecked by my CPUs ability to keep up.
You should have no issues whatsoever.
Out of curiosity, what games are you looking for an upgrade in? And remember that to utilise your current crossfire setup, you must run fullscreen without windowed.
Currently I'm mostly playing BF3, D3 & GW2. GW2 is having some CF issues atm, a new CAP should be out soon I read but still. However, my main reason is for future games and being able to run BF3 on ultra. The 5850 only has 1GB VRAM, this does not stack in CF so I get insane stuttering with textures on ultra in BF3.