Actually, I've been seeing it more often lately in ACE.. but my connection has been crap. I had ATT out to the house and they did some stuff and now I'm much better. BUT I have seen similar as you.
Your vid processing could be killing you. FPS drops equal you not 'seeing' things as quick as others and your hit registry will be crap.. thus you seem to be shooting a person, but they walk up and stab you in the head. The higher the graphic demand (such as air strikes, smoke, and close-quarter-combat with another player) the more likely you are, with a marginal rig, to drop FPS.
I saw a big improvement on FPS when I built a new rig. Later, my DSL signal became crap and I saw similar performance drops with ping spikes. It's always something (lol).