Same exact issue here too. Also in ArmA 2.

Rig:
i7 2600k @ 4.7Ghz
GTX 660Ti
8GB Ram
Windows 7 64bit

Only time cpu and gpu usage go up from 25% and 20-40% is in the main menu (gpu usage at 99%) just after starting the game. Also changing settings from low to ultra have no effect whatsoever. FPS is around 15-40 at all times, with some spikes at 2FPS.