I confirmed what you found yesterday, to some degree.

When I got 5 WoWs up and running, they were running on only 2 cores. When you check processor affinity, they are all on cpu 0&1.

However, by manually assigning them, (I did my main on cpu3, and all the rest on 1/2/3), my framerate nearly doubled. I went from 50 fps to 100+fps on all screens.

My specs:
Q6660
8800GT
4GB RAM
4 alts at 800x600, absolute minimum settings
main at higher reso (1024x, i think) and near max graphics settings.