I would also say that the list of games utilyze more than 2 cores. Honestly with BC2, I can't say how well a duo works though. Personal experiance, BC2 didn't give me anymore then 5fps when setting all the details and resolutions lower. I simply had to overclock my cpu and gpu to get a good performance range, I also turned vsync on and it somewhat helped actually.
Restore the gpu to it's original clock and retry some of the games?