Just to give you an idea, I have a testbed LISTSERV server running on
a P100 (NT of course), 96M RAM, and the difference between bulk adding
(ie with IMPORT) 80K subscribers on Classic and Classic HPO is:

Time to add 80K under Classic:       Was still running when I got home
                                     tonight, had done 75K in 4:23:34

Time to add 80K under Classic HPO:   31.926 sec

Same machine, same code, same list of 80K users.  The only difference
between these two runs was the LAK.  I'm sure very few people are running
production systems on P100s of course :)

YMMV but if you don't have HPO, expect long ADD times when bulk adding
so many people.  I don't even want to think about how long this would
take if you didn't use IMPORT.

See also http://www.lsoft.com/products/listserv_perf.asp if you like
graphs and benchmarks.

Nathan