It sounds like you may be looking at the Max Message Size setting on the Mailing Lists card of the Options page that is accessible by System Administrators. That setting is in KB, and defaults to the value you indicated, while the throttling settings - located on the Priority and Throttling card of the Options page - are in MB and messages per hour. Mailing lists are also subject to their own throttling limits, which is specified on each list's Options page.
Also, keep in mind that throttling limits are aggregate limits. SmarterMail doesn't just look at the size of the message being throttled, but also all other messages sent by the domain and mailing list over the past hour. To estimate how long it will take a mailing list to send out a message to all subscribers, it isn't enough to know the size of the message, you also need to know how many subscribers the message is being sent to.
Andrew Barker
Software Developer
SmarterTools Inc.
www.smartertools.com