Thief Framerates

I have fps issues with the new Thief.

Before I bought the game I tried to demo it by getting a copy from the bay. Solid framerate with little to no stuttering at normal settings. I was sold so I bought the game on steam. When I went on to play the legal copy, my framerates began dropping. Even at low settings it was still stuttering. Any idea why?

TL;DR why the hell is the legit copy stuttering but the non legit copy did not?

FX6300 4.1ghz

HD7770

1080p low settings on the legit one

1080p normal on the bay copy