Well, I dont have much experience with NVIDIA cards, so here it goes, I would suggest uping the performance of the card when VSync is enable through the control panel or whatever of the card, and 300 FPS is outrageous.
As far as Im aware one cant just 'up' the performance of the cards. V Sync sets the FPS cap at 60. So its either 60 when its on, or my cards max out and get the highest FPS possible - theres nothing inbetween. At least from what I know.