Quote Originally Posted by Kicksome View Post
You could use i7 1st gen or higher, and 16-24 gigs ram, a nvidia 580+ video card or higher. SSD drive, enough to hold windows 7 and wow - probably 128 gigs min space.

You'd need 2 of these, each can run 12 copies of wow. Total 24. That's probably the cheapest way to go.
Separate installs of wow does not improve the performance. There is no difference accept more space taken up on your drives. One install can run unlimited number of copies of wow, only that it will probably top out somewhere due to processor capacity.