Not sure if it's been mentioned already or if it is already a well known issue, but I get frequent stutters if I have a browser window running/opened, for example on another screen, especially in the foreground (so when I'm technically outside of the sim), but it's also the case when the sim is focused, maybe only a bit less pronounced. Nothing major or CPU-hungry running in the browser, might just be a single wikipedia tab, but the moment I put something else in front of the browser, like a Plan-G window for example, stutters stop, FPS improves. I imagine, even though most of the time I'm limited by the GPU, somewhere a single thread is trying to carry the avionics/screens in the sim and browser javascript/rendering/redrawing and it bottlenecks the whole thing.