Lagging with 100 FPS.

So when I turn on vsync which limits to 60 FPS, runs buttery smooth. But when I have around 100 FPS on UNLIMITED FPS setting, I get screen tearing and lags a lot. When I'm playing Minecraft on singleplayer/multiplayer I get around 100 FPS. You would think that that enough would run buttery smooth. But no. For example, I have 100 FPS just walking around but when I drop to 90 FPS, I get a HUGE lag spike. So basically what I need is a fix for screen tearing, and a fix for that huge lag spike.