Help for a newsletter ar_mailer the right choice?

Hi, i've to build a simple newsletter system for a client and for the
begin he will have something like 5-6000 contacts (that's how much has
now) and probably he will get to 25-30000 contacts until the end of the
year. Searching on google i found that ar_mailer is good for newsletter
systems. But i didn't find how many contacts would manage without
problems. My fear is that include so many contacts in a table would take
quite a lot (it's not a problem if them are delivered during some days,
but the time to include them in the queue should/must be very low
What do you think? Anyone has experience with ar_mailer (or something
else) and many contacts to manage?