It could be a little bit, I don't know if going to an 8350 would show that much of an improvement. Those Deneb core chips are monsters, especially if overclocked. Try OC'ing it first to see if you notice any improvement.
Honestly I think if you aren't getting the performance you expect (be reasonable) then the only logical conclusion is that its the CPU. The phenoms were phenomenal (heh, wordplay) for a good while. Good price/performance ratio aswell IIRC. Though they certainly can't hold much stock next to an i5. Moving to an 8350 might be worth it since you already have the mobo and would save you 120+ bucks.
But I would look up how to get rivatuner/afterburner OSD to tell you more details, vram, cpu usage, ram usage, etc. I can't remember how though .