>> According to Apple the Q650 uses a 68040/66 and the C650 uses a 68040/50, 
>> at least that's what they posted in their Apple Spec Data Base on their 
>> Web page back in May. No Centris or Quadra is listed that runs at either 
>> 25 or 33 Mhz. They're all either 40, 50, 66 or 80Mhz.
>
>Actually, the number for processor speed that you normally see posted 
>(and the number that I've apparently been using so far in my 
>machine-status document) is the data bus speed, not actually the CPU 
>speed.  However, since I think that the bus is the limiting factor, we 
>might as well leave it that way, unless someone has a convincing argument 
>for going the other way ;-)

Referring MC68040 running at 25/33/40MHz as 68040/50, /66, /80
respectively, is a marketing ploy solely devised by Apple.  I've never seen
a single publication made by Motorola which refers to these chips as
running at 50, 66, or 80MHz.  

68040s have been, using Intel's term, partially "clock-doubled" from its
birth, unlike 486s which later made "clock-doubled".  And I think Apple
tried to make their products *look* faster by referring PCLK frequency
(which is double BCLK frequency) instead of the official "Frequency of
Operation" defined in the manual (which equals to BCLK).  For example, the
raw processor speed of the MC68040/33MHz (referred by Apple as "68040/66")
is considerably lower than that of the "clock-doubled" 486DX2/66MHz, though
I don't remember the exact figures.

Anyway, that's the whole story as far as I know.

ken