Yea, you are pretty much stuck with OEM CPU upgrades or super expensive hard to find 3rd party ones for the MDD. The QS and other AGP G4's have a wide variety of upgrades (I have a 1.25 Ghz single G4 in one of my QS's made bu Sonnet). The layout for the CPU is different on the MDD and I guess the market for high end G4 upgrades died when the G5 came out or 3rd parties had a hard time getting faster G4 CPUs since Apple had first pick for Powerbooks?