Hmmm... So my question to you would be why would you NOT want to take advantage of all your desktop for the game windows?
If I were you, I'd split your screen horizontally and set your resolution via the WoW config file appropriately.
If your monitor is 1920x1200, I'd run with two windows of 1920x600, or maybe make one bigger than the other...
Just don't see the point in having dead areas if there's no reason to... (To each their own of course.)
