Actually I had this same problem with my fx4100 and my gtx560 ! Low frame rate on most games. Low frame rate even in the lowest graphics settings... I tested RAM modules, HDD with SSD, PSU.. The solution only came when I fed my cat with the fx4100 and bought an i5. It's not exactly bottlenecking the GPU.. it was just keeping the whole system back! Now the gtx560 kicks @ss as supposed to do.
The funny part is that I was a big AMD fan for many years!! Anyhow, I believe it's just this model with bulldozer tech and not something more generall.
Ερωσθαι !