However, I did so through upgrading to a larger main screen. This means that my GPU was now driving more pixels , at a greater frequency of. So my GPU, which had seemed fine before for an application as simple as Classic WoW it was now required to be working. It was not sufficient for the task.
Even with all addons deactivated I was able to see that sometimes the game would blink even with VSync off or on. It didn't matter whether my GPU was reaching its limit. Zones like Nagrand, with all of its lush vegetation, would make me push and keep my GPU at 100% which would eventually lead to slowing down.