What exactly is 1-1?

So if I have this right my native on my monitors is 1920x1200. So I can just type in 1920x1200 but for better performance it makes more sense to run the smaller windows at something like 800x600. So I could say type in something like 640x400 for the smaller windows and it will force that window down to that size even though wow does not offer a window that small? Also since 640x400 has the same aspect ratio at 1920x1200 then if I do have to swap the picture will not look smashed or stretched althought a 640x400 window will of course show a whole lot less real estate than the 1920x1200 one.

So if I do want to five box for performance reasons I should set the side windows down to something like 480x300 and keep the main window cranked up. Also set each instance of wow its own thread affinity?