i had random fps drop sto about 2 fps in COD: BO for about 5-10 seconds running a 460 on a 1920x1080 display. let me know what happens when you play BO. I play GRiD on my set up and don't get the problem and will be playin left4dead 2 soon so i'll see what happens then.
COD: BO have lag issues even with good GPU. the problem lies more on the cpu part. do you have dual or quad cores cpu? i heard the lag are much more persistent with dual core cpus