The Hertz on a monitor describes basically how many frames the monitor is capable of showing in a second, so your monitor can show 75 frames a second, unlike the much more common 60 hz, or 60 FPS. So the monitor accepts as many frames as the GPU gives it, whether it's 30 or 180, but it can only show a max of 75 FPS. I don't see any reason in your specs why you should be getting frame drops, so I suggest checking task manager and MSI afterburner to see which is maxed out, and fix accordingly.