I think it would be good to browse through FPS test thread and try to figure out if similar systems perform better indicating that there is something wrong with the setup, most likely corrupt drivers, DirectX etc.
Of course if some other game with as heavy or heavier graphics runs OK it could indeed be caused by the game.
My FPS was around 30-50 with one notch of AA and all goodies on but sliders abt middle.
Intel 9300, GF8800GT.
-C+
PS. The cocpit shadows look very very good and add as much immersion as I though. Maybe a slider to add contrast to them?