mmm, I just tried with aero and dwm on, and full acceleration and it took 2:50 to fill_windows, which is not that slower.
ESC-minimizing took 7s. which is not that slower either(than with acceleration).
I will need to test on XP though for gdi accelerated rendering.
So my reasonning of blaming mdi&gdi might have been wrong.
I am still experience massive freeze spikes(10-15s long sometimes) quite often though, and those dont seem to be justified in any way.(all I have figured about those is that they dont seem network activity bound(no netsplit/quit/join messages when they occur, but that on the other hand they seem very common when typing text, maybe some ime issue?)