The reason verticle sync exist is so that your graphics card doesn't work any harder than it has to. It only works to supply the FPS that the monitor can handle. It makes your GPU run cooler, not work as hard, and last much, much longer.
Like you said, your monitor is only capable of displaying 60 FPS, so why would you want any more? It does you no good at all. But what you do when you turn VSync off is make your card produce the maximum FPS that it can.
That is a very, very, very bad idea. Never, ever do that. That is how people toast their GPU's in record time.
What you basically did was take the rev limiter off a car that keeps it from blowing the engine and put the gas pedal to the floor and max the engine RPM out for absolutely no reason at all.