http://www.everymac.com/upgrade_cards/by_system/powerbook_g3.html

Powerlogix made the upgrades for the pismo in 800,900 and 1ghz

Good luck finding them though.
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PB G4 15" 1.2ghz - Pismo G3 400 mhz - iBook G3 500 "Jukebox"
"SawSmurf" G4 500 - Quicksilver G4 Dual 1ghz modding...