I grabbed the latest sparc tarballs, 19971106, and using a kernel made from sources supped Sunday,, I'm not seeing fifo overruns any longer, but the following has replaced them:

Nov 10 06:29:51 law /netbsd: zstty0: 1 silo overflow, 0 ibuf floods
Nov 10 06:31:00 law /netbsd: zstty0: 13 silo overflows, 0 ibuf floods

Someone mentioned this very early in this discussion, but I've forgotten how to address it.

Brad