It would be interesting to performance test the gcc -mcpu and -mtune sparc specific options on ssh and see if it’s better - IIRC, there are some instruction additions to supersparc and hypersparc (both of which are documented options in gcc(1)) which might help.
Of course, you give up being able to use those binaries on earlier sparc processors, e.g. sun4 and sun4c systems, but if you’re not sharing /usr across NFS (or something) with such systems, or don’t have any, that may not be a problem for you.
The standard NetBSD distribution for a given architecture is usually least common denominator so that it boots & runs on everything, but that won’t take advantage of more powerful features of a given architecture’s “later” revision processors. The older a system, the more important to optimize for speed is likely to be.
Erik