Why is the engine frame-rate limited?

[Eigenmusic]

My refresh rate of my monitor is 60 though...

Right, so your situation indicates that something in the pipeline of game->opengl->gpu driver->gpu->monitor is not working properly; no idea what it might be, and I don't know enough about what could be wrong to help unfortunately.

Nonetheless, your graphics processor KNOWS what refresh rate the monitor is using; after all, your graphics driver is what TELLS the monitor what refresh rate to use.

If someone has their monitor set to refresh at 120 Hz and has v-sync on, I sure hope that their gpu is capable of producing a constant 120+ fps! If not, then the processor is going to be dropping your framerate in order to keep the frames synced. The important thing to note here is that v-sync will sync to the vertical refresh rate (60/75/120/etc Hz), not just 60 Hz; therefore, that is not the problem for you.

Also, thanks MulleDK19 for posting that image; I had wanted to make something similar, but was far too lazy.