V-Sync will just limit the maximum frame rate, prevent screen tearing and on some setups it means a much smoother experience, it will not however have any effect on the minimum frame rate, if its hitting 20fps having v-sync on or off will make no difference.
+1. Unless your FPS shoots up and gets stuck at 60 V-Sync is off and the card is near it's limit and you need to turn down settings or OC.
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