All G4 450s I've come across overclock to 500Mhz, give it a shot
JB

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Not everyone is handy at the fine soldering required to move around the multiplier jumpers. You also need to be careful that you aren't trying to put dual processors designed for a 100mhz bus into a 133mhz bus machine as the overclock will be too high. You might be able to step down the multiplier and put a dual 450 or 500 into a Digital Audio but you still need to be handy at soldering to do it.