I tried all 5 WoWs on a 1920x1200 24" screen, and frankly, the windows were too small to do much with. I now run my main on most of my 24" and the 4 alts on a 20" widescreen. The 840x525 windows for my alts are about as small as I can take, and I plan on getting another 24" to have 960x600 windows. I think that once you get under WoW's minimum default resolution of 800x600, everything has to be squeezed into too small of an area. If you can handle using horizontal span with two equally sized monitors, even if the main is smaller than 24", I'd go that route.