The 1GHz G3 upgrade is a bad road to go down as it slows the machines Front Side Bus to 66MHz from 100MHz. There is a G3 700 or 800 I think for the B&W that far outstrips the 1GHz for performance as it runs at the native 100MHz.
Humm don't you mean the G4 1ghz zif upgrade, those are the ones that slow the 100mhz system bus down in a B&W or Yikes systems. the 1ghz G3 upgrade wont slow the system bus down to 66mhz. it will remain at 100mhz.
the reason the G4 zif CPU upgrade slows the system bus down to 66mhz is cause there is a glitch (or bug if you will) in the controller chip with G4 CPU speeds of 600mhz and above i think

