On the systems I've worked with, Sparc 10 and 20 machines, there was a 
jumper located under the MBUS modules which was either set to 40 or 50.
-Brian
On Jan 10,  4:55pm, Herb Peyerl wrote:
} Subject: Re: Ross question
} buhrow@lothlorien.nfbcal.org (Brian Buhrow)  wrote:
}  > 	I think the versions we upgraded to in the Sparc 10 and 20 machines
}  > we converted were R2.25 and higher.  Lower numbers, like 2.15, didn't cut
}  > it.
} 
} just checked:
} 
} SPARCsystem 600MP Series (2 X CY605B), No Keyboard
} ROM Rev. 2.5, 128 MB memory installed, Serial #4197491.
} Ethernet address 8:0:20:f:44:95, Host ID: 71400c73.
} 
} how do you configure the mbus speed?
>-- End of excerpt from Herb Peyerl