I might add that VSync syncs to some "milestones", so if you are running at 60 FPS and drop below it, even just 2-3 FPS, Vsync will instantly sync to 30 instead, giving you 30 FPS. If you drop below 30, you lock to 15 instead. So if you can just barely manage 60 FPS, and drop below it quite often, you might want to turn VSync off, or you will likely be stuck at 30 FPS most of the time.