Just a quick point to ponder, I have two SGI PowerSeries machines in my
living room each with 6+ R3K cpu's. IIRC they were the first SMP Unix
boxes in the general market (model-wise, not these specific boxes),
and under IRIX5.3 did a sterling job.

I'm not sure precisely which model R3K is inside, but I take this as
an indicator that SGI found at least some way of doing efficient and
reliable locks within the kernel.

I'm London-based, but if anyone would like to take these off my hands
for development work they only have to come get 'em. (they are in deep
SGI 19" racks, being VME based).

Just a thought.

-- 
-Mark                   ... an Englishman in London ...