Update for Neil: I have found that your new algorithm for handling multiple monitors with Moving Wallpapers works GREAT with multiple monitors on the same display adapter. It is very efficient with dwm.exe cycles.
However, it still suffers from the same problems as other dreams when working with monitors on another/second display adapter.
In those cases, it is still preferable to run two or more separate instances of Moving Wallpaper, one per monitor, in order to optimize the hardware acceleration per task per monitor (layman's description).
Because of this, I am now running Moving Wallpaper, Photo Dream, and Desktop Collage on a single desktop comprised of three different 30" monitors using two different display adapters and the (NOT state of the art) machine is VERY responsive - and stunningly beautiful!
You are the man. 