meaning of zimbraImapNumThreads in detail

[gettyless]

the default of zimbraImapNumThreads is 200 - so I'm guessing this means 200 concurrent threads. So, in my Thunderbird 2.x -- the "maximum number of server connections to cache" defaults to 5. Is there a one-to-one relationship between thunderbird's "maximum number of server connections to cache" and zimbraImapNumThreads?

Hypothetically, things should go bad if I somehow had 40 concurrent Thunderbird users looking through their inbox each time, right? Or maybe they have to be moving or deleting files concurrently.

I notice that there was an old thread for ZCS 4.x where someone claims he had to raise zimbraImapNumThreads to 1000 for 120 users (where most/all were on IMAP):

IMAP goes down 2-3 times a week, tomcat restart necessary

... does that sound right for zcs 5.x?