You should turn off Ubersampling that really strains the GPU. Play the game after that it should run fine. If it still slows down then turn off SSAO it should be fine after this. Also get the patch if you bought the retail version the patch helps alot.
I'm having the same problems, the game is playing ok on ultra with ubersampling off with the nvidia 275 beta drivers. Only problem is when I look at afterburner it says GPU 2 utilization is 0%. I tried the workaround where you paste the new value into nvidia Inspector, but that hasn't worked. Any thoughts, I'm around 20 fps in cutscenes and 40ish during gameplay.