My experience was initially as yours; foreground fps off, vsync on, hiding WoW, switched to another app. I just tested with the Oribos character and changed one variable and turned vsync off. The formerly rapid memory climb slowed similar to the SW toon. However as soon as I switched to another app/hid WoW, I hit 160GB memory use and crashed in less than a minute. This was with vsync off. So there are definitely some variable symptoms in this problem.