I have also problem with speed of screen switching between WB and Dopus (or Cygnus). It takes 3 seconds to redraw it!
My guess:
Single 1280*1024*32 screen takes 5242880 bytes of video memory. Mediator can see 8MB window of the memory at the time. If you switch between two such screens, Picasso96 must swap some display memory to make it happen. With the poor bus speed of the Mediator, it really can seem a bit sluggish.
