a G4 is a G3 with altivec. IBM made the G4s from around 450-500MHz for apple because Moto. for whatever reason couldn't produce them at a high enough clockspeed. IBM still makes the G3, (a 750), and IBM does say that the processor can accept a FSB of 200MHz. But the stopped increasing production at a higher clockspeed. The highest it goes up to is 900MHz.