Performance on the MDD was way ahead of it's immediate predecessor, the QuickSilver, these were the big changes;
QS: 1GHz CPU, 1.5GB RAM, 133MHz Bus
MDD: 1.42GHz CPU, 2GB RAM, 167MHz Bus
While it was faster, heat was a challenge since the case didn't properly account for the thermal envelope of the faster G4 (All GHz G4 models had cooling issues but MDD was especially bad). There was nowhere near enough airflow so it used obnoxiously loud fans, so it gained the nickname "Windtunnel". There were 4 holes for intake and lots of tiny exhaust holes.
It would be like shoving an 8-core i9 into a case meant for a 4-core i7. (Does this sound familiar? Intel 16")