What's your FPS with all graphics settings in WoW set to minimum on all toons? WoW @ Ultra is still a graphics pig. Lower you settings to minimum and then slowly bring them back up till you have a reasonable trade-off between FPS & look&feel.

Also, SLI bridging is a waste of time with Wow. You'll get much better performance dropping SLI, putting the main's monitor on one card and the slave's monitor on the other.

PS: Go Beavers