when you want to run 5 at once.. and you want to see them.. you will experience decreased fps due to all the other windows pushing frames as well.

additionally, you will experience another drop off in fps due to the other wows attempting to render the scenes.

the best way to optimize would be to set your maxfpsbk to between 5 and 10 (fps performance on the background, non-active, wows doesn't matter.. so, the lower the better).. and set your maxfps to between 24 and 30 (24 == movie quality, 30 == tv, standard def). after that, tweak for your preferences and hardware capabilities

i'm on an amd 3800+ 2.2 GHz single core w/ 3G of memory and a 8800GT OC. i'm am currently 5 boxing on dual monitors, each @ 1280x1024 and getting 5/30 in a 1 + 2x2 maximizer layout. when i'm doing pve, no problems... orgrimmar is a bit tough.