I have a 280 GTX also.
My FPS never drops below 60 but the in-game physics and movement freezes like above.
This is making the game unplayable.
If I change the graphics options and apply (For example change from High to Very High) it goes away for about 60 seconds but then comes back.
I am running an I5 750 clocked at 4ghz.
My machine runs everything else I throw at it, going to try different drivers and see if I have any luck

Mizaun, it sounds like your issue is related to low memory, slow hard drive access or lots of background processes running.