cpu clock is completely controlled by the main board.

the full 040 i have installed says 25 mhz right on it, probably from a q700, its running just fine @ 33 mhz,

you can do more soldering, and get an oscillator, to make it run at 40/42 mhz.

here is the apple fritter article:

http://www.applefritter.com/node/20510

another Q605@40mhz article:

http://mail-index.netbsd.org/port-mac68k/2002/05/31/0006.html