There is not yet a really good discussion of kernel differences.  The 
best place to look is in the mailing list archives on ftp.netbsd.org, 
actually, but this requires a lot of digging, unfortunately.  The other 
option would be to dig throught the source code to see what's in there 
(ouch!).

There are about 3 or 4 common types of kernels out there tho:

GENERIC (w/ low numbers):  these are compiled by Allen Briggs and are 
basically just -current ksrc compiled with the GENERIC options

GENERIC (w/ high numbers):  these are the pretty much similar to Allen's 
kernels, but compiled by Steve Allen instead.

NFS: these are GENERIC kernels with NFSSERVER turned on, compiled by 
Steve Allen

ADBTEST:  these are kernels compiled by John Wittowski.  They have 
support for the new adb driver which allow many machines to run which did 
not run before.

SBC?:  these are kernels, probably compiled by Scott Reynolds, which 
include his new sbc scsi driver.  the new driver is supposedly slower 
than the ncrscsi driver, but probably more stable (although it appears to 
have hosed at lease one user's machine).

You will probably want to compile your own kernels, though, as you can 
get a slimmer kernel that is tailor-made for your machine that way.  
There is a kernel-compiling howto on www.macbsd.com, which I should be 
updating soon to include a partial list of available options.

I hope the answers your questions some.

Later.

-- 
Colin Wood                                      ender@is.rice.edu
Consultant                                        Rice University
Information Technology Services                       Houston, TX