Not every game uses resources the same. It sounds to me like your GPU is the bottleneck in BF3, and your CPU is the bottleneck in MW3. Since you have a 955 you should try overclocking it and see if more of your GPU is used and if you get a better FPS.
it cant be bottleneck in bf3 as it uses 99% gpu power all the time in that game its just MW3 that it only uses about 40%. MW3 is the only game that doesnt use most of the power also my cpu is oc to 3.9ghz prime95 stable