I've got an archive with an MBox File that looks to be about 45-46Mb. I thought it was 91, but that was because I'd done two exports into the same directory.
I've exported based on email addresses and labels my rules setup, but I think it is a reasonably complete list history from 2006 to a few days ago.
For those who want a decent tool to browse such an archive, not fancy but functional, for Windows, see here:
I'm part way through reviewing the archive now. I had hoped to have it up by today, but some other family stuff has eaten some of that. I should finish and get it posted for pickup in the next handful of days. I just want to make sure the capture didn't pull in non-list traffic that happened to include some references.
I'll post to this thread once the archive is available for pickup.
PS - Thunderbird -> PITA! I had to define a working email address to allow me to see parts of the interface that would let me import an .MBOX. So effectively there is no way to use it as an offline mail reader without an active email account defined. And with IMAP, no way to get it to stop connecting. The tool above seems to be more what was wanted.