Wow looks like crap and runs like a piece of pee. The shadows don't look great and don't make a huge difference, turn them down, it will look almost identical, the things that "make" a game, are texture and other graphics settings, the crap shadows barely register compared to the other settings.
Personally I can run 5 copies on a 4Ghz P2, with a frame rate limit on to cap the main screen 1920x1080 to 60fps and the 4 1280x720 windows, to 15fps(because I barely look at them, whats the point.
My 5850 at stock rarely goes above 60% usage, and my cpu usage is around the same.
FIVE copies, only on two screens which are downsized windows but rendered at higher res then scaled down. Sorry but its a very old game that any newer card will run with ease, if you can only get 30fps with maxed shadows on a 5850, somethings wrong with the setup, ok might be different in the end game zones and you'll have more issues in an ultra busy raid. Theres nothing taxing about WoW and anyone who thinks there is, is barmy.