The price difference i believe is that the X2 4400 gives you 2.2GHz stock while the Opty 165 Offers 1.8 stock. But i like to think of the Opty Downclocked because it can easily hit 2.2Ghz at no voltage adjustments. You cant go wrong.
Whats there to think about. Go for that setup i just posted. Im almost certain most of the ppl here will agree with me. You'll get great performance from it.