Hi, I have a Gigabyte Gtx 670 with the same problem. I guess the "Adaptive" Vsync simply doesn't work. What you can do is to turn on only "Vsync", that will solve the problem. Nvidia really needs to work on the "Adaptive" vsync. Otherwise, that's just a marketing tool.
I'm sorry to reply to you so late because I didn't know your reply. You can try to turn Vsync and tripple buffering on in the Global settings of Nvidia Control Panel. Hope this helps or please ignore this message if you already solved the problem.
I have a GTX 650 Ti from MSI i get screen tearing to the max when i view videos/youtube only way to disable that is enable Aero and Desktop Composition to enable desktop vsync. But for games Guess run the game on full screen thats when adaptive vsync uses it not sure but my next card im buying is a ATI if i knew about the screen tearing i would of not bought nvidia.