Same issue. Makes no difference if i play on 800x600 res and everything LOW or 2560x1600 res and everything ULTRA.
FPS remains the same regardless of resolution or graphics settings. Playable 30-45fps Single player but dreads on MP.

i7 2600k @ 4.6 GHz
Evga GTX 680
8GB GSkill 2133Mhz
2 x Crucial M4 128GB SSD Raid 0
Windows 7 Ultimate 64bit
30" Dell U3011