I dunno if it's been discussed, but I've had alot of luck with the Ultimate Bulletin Boards.
I don't know if their code is written any better then the WWWThreads ones, but every board I have ever visited, that has serviced extreme high volumes of traffic has been running UBB.
I belive it comes in a varity of programing languages. (PHP, SQL, PERL.)
Maybe the big boards I've been on have just had more server behind them?
Anyways, it's an option. (maybe?) and it has all the same or similar features that this board currently has. I've used the administration system on it before, and it's very simple to setup and administer, yet very powerfull.
I don't think the databases would port over to the new code, but that's no big deal, people would just have to re-register. (Happens eventually on every board when the s*it hits the fan.)
I thought I'd just throw this up here as an option.
Send me an e-mail if you have any questions about it.
Ultimate Bulletin Board. http://www.infopop.com/