I got a G4 upgrade from Fastmac, the advanced upgrade. Came with no instruction, so I just pulled the tape off of the core, screwed the heatsink on, and called it done.
Then I noted the fan revs up to high speed any time anything remotely taxing happens.
Figuring the thermal transfer was no good, I got a Shin Etsu thermal pad. Pulled the heat sink off, totally cleaned the old pad off of the heat sink, cleaned all of the current crap off of the processor, and applied the Shin Etsu thermal pad.
Wow, what a difference. Lots cooler all around, even a small bit underneath. I'm convinced it's making a big difference, and so far no high speed fan.
Tom