Not sure about the overclocking part; a company who had been in business a
relatively short time and offered a logic board replacement with upgraded 1.9
GHz G4 chip; & was a board-for-board swap, for the most part. Hard to find now.
•Daystar CPU upgrade - iMac G4 flat panel:
http://www.barefeats.com/imup.html
The inaccessible design of these iMac G4 luxo model computers makes for
major difficulties compared to simple open door case tower model G4/G5.
I remember my B&W G3 350 had a way to be overclocked by changing how
the pins on the processor connected. That was another era. Some even had
zif adapters; users worked around the limitations, because there was room.
My iMac G4s don't exactly function, One was able to start but needed the
superdrive replaced, or so it seems. Another may need a power supply,
or it appeared. The Third one was part of a deal where I had to take it to
get the one I wanted that worked OK at the time. Likely it has good parts.
Although this http://xlr8.com/machspeedcontrol-osxandos9combo.aspx may
be a little interesting, that's all remaining from the XLR8yourmac Daystar link.
A CPU upgrade and maybe an SSD such as OWC has for legacy ATA Macs?
Could be there may be some way to upgrade the processor, if you start out
with a pile of repairable iMac G4 1.25GHz 17" or 20" models, and a box of
other items. There is not much room on an iMac G4 logicboard, but maybe
a CPU from a portable Mac may be able to work. Trial & error, & error, etc?
Sounds like a project, of a sort...
Good luck & happy computing! 🙂