Toms hardware has asked Nvidia about the problem:
'Nvidia Responds to GeForce 600 Series V-Sync Stuttering Issue
Nvidia provides an official response to the reported v-sync stuttering issue with its GeForce GTX 600 Series
Tom's Hardware has received several requests to look into a v-sync issue that a number of owners are seeing with Nvidia's new GeForce GTX 600-series graphics cards. A number of readers have pointed us in the direction of a very long forum thread where multiple customers express concern over stuttering problems with their Kepler-based graphics cards.
Our editorial team played through a number of games with GeForce GTX 600-series board and was unsuccessful in reproducing the issue. As such, we're fairly confident that the issue does not apply to every configuration based on Nvidia's newest cards; some folks are experiencing it, while others aren't.
Eager for an explanation, Tom's Hardware reached out to Nvidia for its response, understanding that owners of $400, $500, and $1000 graphics cards want to know why their boards are misbehaving. The company sent over an official response to the GeForce GTX 600-series stuttering issue, which reads:
We have received reports of an intermittent v-sync stuttering issue from some of our customers. We’ve root caused the issue to a driver bug and identified a fix for it. The fix requires extensive testing though, and will not be available until our next major driver release targeted for June (post-R300). For users experiencing this issue, the interim workaround is to disable v-sync via the Nvidia Control Panel or in-game graphics settings menu.
Although that's not necessarily the most reassuring message, we're at least glad to see that Nvidia has identified the issue and is working on a fix. We'll update you if we hear any more on this, so stay tuned!'
http://www.tomshardware.com/news/GeForce-GTX690-GTX680-GTX670-V-Sync-Stuttering-Fix,15670.html
Hopefully Nvidia do get it all sorted out by June.