vsync always completely took care of it. The point is that it also has some pauses/delays/stutters, especially if the card isn't able for very high FPS (regardless if it's locked to a vsync at that time, it's the 'frame time possible' that matters ..but that's details)
No no no no no no no. G-sync must absolutely give equal or approximately equal hz to the fps. If it's lower or higher there will be artifacts, and I suspect perfection will not be possible, but it's probably close enough to be unnoticeable.