Peter Hufnagel writes: 

>>> For NetBSD, or SPARC systems in general.  mbus.sunhelp.org claims you
>>> can mix different speeds, provided the cache controllers have the same
>>> major rev, and you don't cook too much with the extra heater, etc.
>>
>>SPARC systems in general.
> 
> We had a Sparc20 at work that had (I believe) a SM71 and a Ross
> Hypersparc 125Mhz in it, and it worked fine under Solaris.

Didn't we have this discussion a month or so ago? 

As I recall, the conclusion was that you can put all sorts of bizarre 
combinations of processors in the SS20 (I had one that ran Solaris in 
production for a couple of years with a dual 100 Ross & an SM71).  However, 
if you have a problem, don't ask for help.  It's a completely unsupported 
config, with far too many strange possibilities to debug. 

A google search should turn up the thread. 

Ken