Game Stutter on movement

I’m going to thank Meat5000 in advance for answering this :)…

Why does a game stutter (slows down and returns to normal) in some area’s of a game even though the framerate doesn’t drop on a powerful desktop? We are talking I7 3770K’s with 32GB of ram on a 64 bit OS, finally AMD 7970’s for GFX.

Surely performance shouldn’t be an issue with machines that can run the likes of Witcher2 Maxed out with no performance issues?

Yes VBL (Vsync is enable), if not screen tear happens.
Yes I have played around with AA, although for them type of machines it shouldn’t be an issue.

Maximum Allowed Timestep, in Time Manager from Edit Menu Project Settings allows you to set a minimum allowed FrameRate below which FixedUpdate is cut short to allow the main thread to run. This results in the slowing of animation and mechanics and other spurious effects that occur from code in FixedUpdate, when you go below the threshold.

Altering Max allowed timestep will change the threshold. Playing with Fixed Time Step will determine how many times fixed loop is executed per second and may need to be altered so it’s not executing too many times for each frame. Also, if you don’t require so accurate physics, turning down the iteration solver count can help alleviate the problem.

http://docs.unity3d.com/Documentation/Components/class-TimeManager.html