Dual View: GPU Choice

I'm currently running a samsung 19" @ 1280x1024 (for windows/movies/music desktop) in dual view with an asus 22" @ 1680x1050 which I use as my gaming monitor. Its an expensive alt-tab solution :roll:

Im choosing a new graphics card for my new rig (E6600) to power all this- Im thinking either 8800GTX, 8800 GTS 640mb o/c or 8800 GTS 320mb o/c. If it was just one 1680x1050 monitor, I am thinking either 320 or 640mb GTS will suffice. But in dual view, Im assuming that there will be a big overhead and the GTX may be the way to go.

Any opinions / dual view benchmarks gratefully received.