LadyWYT

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Does it look like this? Maximized Borderless only removes the white border from the box the game runs in if you have it windowed. If you run a two monitor setup and want to click off the game screen for a moment without the game minimizing, but don't want to see the Windows taskbar either, try Fullscreen + Always On Top. That should keep the game running fullscreen on one monitor without minimizing if you click on the other screen for a moment, without the taskbar getting in the way of the game screen.
Now if you do that and the Windows taskbar still insists on including itself in the game screen, I would check your settings on Windows taskbar to make sure there's not something there causing an issue.

Okay, I think I've completely solved the issue now.
The majority of the issue was caused by a missing chipset update for the BIOS, which caused the mouse movement to drop the fps(I presume because it was putting unneeded loads on the CPU). Updating the chipset solved this part of the issue, but there was still some subtle jitter leftover.
After much poking around with the settings, the rest of the solution was dropping the Max FPS from 75 down to around 30. The frames run jitter-free now!