> i read that the MDD Mac can't use the PC2700 ram at full speed only at
> ca. 50% off the speed.

That's only true for the G4 CPU itself. See boot_wb's answer.

> So how big is the performance improvement of the
> MDD over the 2002 Quicksilver?

https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=6910&forum=11#71009