I had that prob as well till i used maxfpsback set to 8 fps on all and
maxfps set to 60 was getting 50-60 fps out side of major citys on me
main wow instance in duel view

i have 22" viewsonic as main and 19" viewsonic as second



just upgraded from 8600gt NVidia to 8800gt gona try duel view again and see how that runs now.