I'm having similiar issues. My FPS doesn't change at all when changing from Low/Med/High, but using PerfOverlay.DrawGraph 1, I can tell my CPU usage is very high, similiar to the original problem people were having the beta.
My rig is:
Phenom II 940 Black Edition 3.0 GHZ
4gb ram
Nvidia Geforce GTX 650Ti
I'm not expecting 60 FPS on Ultra or anything like that, but shouldn't I -atleast- be getting in the 50-60 range on Low/Med? I can actually get -decent- numbers on Test Range and slightly worse on Campaign. The minute I jump on MP though, I start topping out at like 30 FPS on low...which is pretty unplayable.