http://www.geforce.com/whats-new/articles/nvidia-geforce-304-48-beta-drivers-released/
quote:
On the GeForce GTX 670, 680 and 690, some users identified an occasional micro-stutter when gaming with VSync or Adaptive VSync enabled. For most this wasn’t noticeable, but we take any issue that detracts from a user’s enjoyment of our products very seriously, and have introduced a fix that will improve the smoothness of VSync gaming.
the driver update worked. running smoothly now on gtx 680.