ok.. i had a thought. the fps number you are looking at is actually the number of frames per second wow is pushing data to the card. this does not mean, that its the number of frames per second drawn to the screen from video memory (it's been years since i've played with the inner workings of directX and video memory). the double buffering may not be happening as often as you think.

run dxdiag and look @ the display tab. try running the tests.. see what they come up with.

right now, i'm leaning towards driver issues.

here's a thought... put your 2x2 of alts on the 'slow' screen .. and put your big main region on the other screen... see if the alts get choppy