XSoloDolo :
Peter Cytryn :
not much. You get a better physics score in 3dmark, but the increase is hardly justified by the upgrade Price. I have Phenom II x4 965 and i will not be upgrading at the moment. Óverclock your CPU and use your Money on better GPU - it will be better spent, and THAT will give you more FPS!
Here is a direct comparison between the two: http://cpuboss.com/cpus/AMD-Phenom-II-X4-965-vs-AMD-FX-8350
So this brings me to another question do you think X-Firing a 7850 would be a wise decision? and my cpu is oc'd @ 4.0ghz
Some people don't like CrossfireX so you might hear those kinds of opinions (rarely based on having properly used such a system of course and usually an opinion based on something they read online from someone else). Personally I like CFx. It has never given me any real problems though there are some frametime issues (a lot of that fixed with the latest BETA drivers and set to be even further improved with the next driver release).
I'd say it is worth it. If you CPU bottlenecks the two GPUs it's not really that much of a problem seeing as it still allows you the chance to use higher AA and AF settings without incurring any performance losses.
My 2 cents.