Original Post: I have noticed flickering issues, however, I would not hesitate to declare it full-on studdering. It's a recurring issue, which makes it difficult to pinpoint. But it was getting to WOW TBC Classic Gold the point where it was making me angry, which is why I attempted to investigate what might be the cause.
Short story, it is only recently that Windows permitted multiple monitor refresh rates for nearly 13 years, Microsoft seems to have fixed a commonly-discussed issue with regards to how Windows handles multi-monitor refresh rates. For a long time, Windows 10's Desktop Window Manager (DWM) created frame-skips and stutters operating multiple monitors at different refresh rates. This issue seems to be fixed by Windows 10's DWM 20H1, which supports hardware-accelerated GPU scheduling (WDDM 2.7). A Reddit user demonstrated this feature.
As soon as I spotted this issue I switched from having a 144hz main monitor with another 60hz monitor. I now have both of my monitors to 144hz. This was due to the fact that I did not wish to change my system, and my 60hz monitor was due for an upgrade.
However in doing so I upgraded to a larger main display, meaning that my GPU was now processing much more pixels and both at that high a rate of refresh. The GPU, that was fine in the past for something as simple as Classic WoW but was now having to be working. It was not up to buy WOW TBC Gold the job.