>With the qualifier that the MDDs (like that of the thread opener) can only be upgraded up to (dual) 1.8 GHz 7447A.

Yep, only older PowerMac G4's will accept 7448 upgrades.
So...as the original poster has realized by now...we circle back again to the PowerBook.
Thank, btw, for the information about the 1.33 GHz iBook's gpu.
My current iBook is a 14", and I would be willing to trade a little speed for a smaller laptop.

My first PowerMac was a Quicksilver model, and at 9333 MHz it still had enough power to run MorphOS quite well.