if you ran 5 wows on the same machine, all @ 1600x1200... then they were stacked. the ones not showing were not impacting your performance much at all. lay them out side by side, not overlapping, and see what you get.

how many displays are you using?

pip swap does move memory around and in some cases, will re-render surfaces pushing the cpu/gpu harder and dropping your fps. this is within wow and out of my control. if you are pip swapping from one graphics card to another (my situation) then you are moving the graphics memory between cards... a fairly pricey operation. (i have wondered if you would get the same effect if you were using 2 displays on one card...)