My record is 12 WoW's playable on 1 pc, with a slightly out dated pc.
At 16 WoW's massive screen tearing occured in some windows, but still ran smooth, unless I entered a city.

Used RAF to try this with on a live server. Set my nvidia settings on low(so on the card itself, not just in wow) and used keyclone to set CPU core affinity.

framerate was more then ok and all looked good + moved ok...

Just my test experience... Enjoy 8)