Phenom x4 850 @3.3 Bottleneck?

No it's not a bottleneck for the GPU you are just more CPU bound in relation to games that rely heavily on the cpu.

Check out this link.

http://www.ocaholic.ch/modules/smartsection/item.php?itemid=817

Your performance should be quite close to the Q6600 @ 3.0GHz likely a little less due to the lack of cache.

However a new CPU is a good Idea unless you can keep going with the overclock.

What motherboard do you have?