i had some issues with lag,skill lock up,wep swapping for the last few months. it took me buying a new computer to find out the problems.
open your task manager and see whats cooking in there once in awhile. i found some background windows programs that seemed to be holding my comp back.
the 3 major culprits were BITS(background intelligence services) superfetch, and windows search.
search is iffy on whether or not you want to keep it going,i would start with the first 2, they slowed things down that it made a difference turning them off and running large groups in game.
you can find them in run-services.msc
stop them then disable
then make the comp take no action under recovery.