Dropping in a faster processor speeds up a Mac only if the Mac has been designed so that the processor (or the daughter-card that carries the processor) controls the system bus speed, directly or as a multiple of bus speed. That isn't so in the Q700. Your faster processor is confronting the original 25MHz oscillator, and loses the battle. Even if you replace the oscillator successfully, there is no guarantee that auxiliary chips on the logic board can cope with a higher system bus speed. If you search the literature you will find out what others have achieved in trying to 'overclock' the Q700.

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