At present the list is just short of 500, but new signups come in about ten a day, so realistically it's going to have to cope with thousands rather than hundreds. I'm reassured that you think Mail::Bulkmail is sound. I wonder why nobody's maintaining, given that it meets such an obvious need.
I've just recently used Mail::SendMail to send out 600 invitations and reminders for a graduate research survey. It took all of about 5 minutes or so. I've had no problems with it yet. I'd be interested in knowing what the magical cutoff point is--just in case I have to help someone with a larger mailout.