(Solved) FPS issues in editor - Switches between 10 and 60 depending on highlighted window

I have a high end laptop (gtx 1070 8gb, 32gb ram) and working with the editor spread in two monitors. One with the main viewport and the other with particles and materials.

I have a blank scene with only a simple particle on it - while I have the main window selected, the performance is very sluggish, around 6-11 fps. By just clicking on the particle editor on the second monitor, without doing anything else, I get smooth 60fps on all of the rendered windows.

Does anyone have any idea why?

Solved! It was just G-Sync being enabled on windowed mode.