From my point of view -
The real problem starts to happen when an individual post thread starts to run past (and here's where it gets tricky to calculate, but on average) 100 or so. MySql can be problematic with large table entries, (as we see here, some threads running to 2000+ replies). The problem is that SMF uses a single database for all its data, and ALL posts (no matter what Board they are in) go into a table called (by default) smf_messages. That table gets pretty gosh-darn big, and that's a big part of the problems we see here. (Meta Clubs and OT activity are at the root of a goodly portion of our issues, the other issue being hosting costs (as in we could have a bigger better server space, and that would help, but as my auld gaffer used to say 'Aye, lad, brass!')
I can see that there is a user community here that uses and enjoys Meta Clubs, and OT, and I can respect that, even if I don't agree with that view. What I would suggest is that we look at a compromise that would keep the server and our users happy. What that would look like, would be open for discussion, perhaps it would take the shape of a "rolling 30 days" worth of posts per board, perhaps setting limits on the number of posts in a thread, and "rebooting" the topic once that limit is reached. At this point, I think though that we'd all agree, that board reliability and performance has suffered, and that we really should do something to try and get things back on an even keel.
If there are suggestions on how to keep Meta Clubs and OT alive, and not impact board performace as well, I'd be happy to hear them..
Cheers
Harold