above 600Mhz i would say yes, it seems that at that point that the heat output gose up exponentially with the freq increses, this may be due to the V increse required to do so
to get your Z to insane speeds you would have to switch over to active (ie consumes power) cooling, may be fun but not nice on the battery
i have aleady cut up my case to add 2 usb ports, i may as well cut a bit more and give it a go, i dont expect to see much of an improvment but it will give me peice of mind
i will switch over to cacko and see what i can get it up to and apply the hack, i have to reflash OZ anyway to boot off the second CF slot (i put the usb ports where the microdrive sits)
note with the cxx00 series there should be enogh room for a small stich on heatsink as the PCB is about the thickness of a CF card from the outside, i have a nice stick on heatsink i used on my NSLU's thats just the right size and shape, if you are in australia jaycar sells them.