Performance drops as the game progresses...

[MercenaryForHire]

Hey Creep. You're not alone - I'm having the same problem. Does your framerate also take a nosedive during combat?

See my thread here:
http://frictionalgames.com/forum/showthread.php?tid=937

My PC is about the same spec as yours, but with a beefier video card (6600GT)

What version of the NVIDIA drivers are you using?