If you upgrade the CPU, go with the 1.42GHz dual. That way you can get the speed of the fastest MDD ever, without giving up OS 9.

The MDD came in three revisions:

2002(FW 400):

G4/867 MHz dual,

G4/1.0 GHz dual,

G4/1.25 GHz dual

NO OS 9 January 2003(FW 800):

G4/1.0 GHz single,

G4/1.25 GHz dual,

G4/1.42 GHz dual

June 2003(FW 400):

G4/1.25GHz single

G4/1.25GHz dual

Your model and cpu are in green. You can swap your cpu for any in blue, the bold being the fastest. This is a common way to get the faster (or dual if originally single) cpu and still be able to boot OS 9.

Hope this helps