The 7850 is not so much more powerful that it should bottleneck on a 955. They are fairly decently paired to each other.
If your games aren't performing as well as you'd hope, well your tech is a little behind the curve at this point (CPU more than GPU). If you have a AM3/AM3+ board you could go to an Fx-6300. Otherwise you should switch to an intel board when you want to upgrade. Or hold of until 2016.