I was doing a very casual testing of my personal Opteron 165 overclocked to 2.6GHz, and a 3800+ X2 overclocked to 2.6GHz. Besides the L2 cache, the systems are pretty equal.
Playing Battlefield 2, I noticed more jerkiness with the X2 3800+. Probably a slower FPS. I do have 3Dmark06, I think I'll compare that.
Thanks