Make sure you are running in Fullscreen, not Windowed Fullscreen. For me the game has a habit of resetting to Windowed Fullscreen every now and then, I've yet to understand exactly why and when.
Anyway, Fullscreen runs like a champ for me with the proper settings. Windowed Fullscreen on the other hand displays a clear stutter when turning the camera, at least in some locations.
Strange that I'm getting the behaviour you experience in windowed fullscreen while I'm running in fullscreen. I suppose I'll have to try windowed fullscreen tonight and see if the problem goes away!
Edit: An article on Kotaku says disabling the UPlay in-game overlay can help resolve some stuttering and mouse input issues. Gonna give it a try tonight.