I recall going to 1.067 Ghz was the easiest in terms of resistor placement, but overclocking Powerbook CPUs is not dependant on cooling, as it isn't that great even if the fans run at full speed. You either get a decent overclock or you don't. I'm currently fixing up some Mac Mini G4s (the final 1.5Ghz versions), first one @ 1.67 the other @ 1.83Ghz no problems. The one at 1.67 refused to do a thing @ 1.7 or 1.8 Ghz settings, so I'm lucky the lower speed worked as I had to remove (and lose) a resistor on the top side of the board (not sure if 0K or a particular ohm value).