Hello John

Thanks for the elaborate answer. I have compiled a vm with an 
outcommented QDFlushPortBuffer() and found out:
1. this is where the time goes (now it's as fast as OS9)
2. like the (I assume it was yours) comment said: video becomes jerky 
(at best).

A quick search at apple lead me to  TN2051. There's a code fragment 
that could lead in the right direction.

In a first test (FreeCell 1) video becomes animated again but window 
movements still leave artifacts.

karsten