The reason you're probably getting low FPS isn't because your CPU isn't fast enough -- the Phenom II's are rather peppy -- it's because your CPU has only 4 logical threads. Dolphin makes use of two cores, which makes Intel chips ideal; specifically the i7 because of the complex core technology. These chips (like a Sandy Bridge i7) have 2 logical threads per core, effectively allowing 4 core processing on the two core allowance from Dolphin. With what you have now, you'll have to buy an entire new Mobo and possibly RAM (if you have 1866 or better) just to change out your processor. Overclocking appears to be your only, repeating the previous posts, and best option. You'll need to just tinker with it and hope for the best. There are alternatives, but most are extremely dangerous and risky for just a small profit. Either way, your GPU is amazing, so keep your graphical settings about mid-range and enable all the speed enhancers you can to keep your frames up.
Good Luck!
Edit -- The i5 I have claims to be Hyperthreaded, but that fact has been thrown into question. Replaced i5 with Sandy Bridge i7.
Good Luck!
Edit -- The i5 I have claims to be Hyperthreaded, but that fact has been thrown into question. Replaced i5 with Sandy Bridge i7.