[snip]

> Ideally, I'd like to see the following kernel options (as well as any other
> relevant ones I've missed) explained in such a way that someone who hasn't
> read any of the kernel code can correctly calculate (not guess) the values
> they should use:
> 
> NMBCLUSTERS
> NKMEMPAGES

I guess you mean NKMEMCLUSTERS?

> BUFCACHE
> NBUF
> BUFPAGES
> 
> It would also be useful to know the default value for each option for
> macppc, the interactions between the different values, and any other
> implicit limits (i.e. what particular limit gets exceeded that causes macppc
> machines with 1G+ of memory to panic on boot).

Well, to know the default values for your platform use the
sysctl command, to have a more detailed explanation use
man 3 sysctl :-)
or man options is also gonna help.

Btw, as i understand, in the GENERIC kernel config from macppc,
there is allrdy :options	NMBCLUSTERS=1024
Or you can look in:

arch/macppc/include/param.h

But plz look in man options, NKMEMCLUSTERS, BUFCACHE, NBUF and BUFPAGES 
are explained there.
Perhaps you also wanna look at KERN_MAXFILES, the amount of maximum
open files that may be open on your system, important if you wish
to run a big mailserver for example.
Bye,

Mipam.