I know you said you didn't want an open source forum, but you do like the perl monk forum. Did you look at the "Everything Development Company". They are the ones who wrote this engine. It is highly customizable and very powerful. Their link is at the bottom of this page. There are several implementations of the forum that you can reach from their home page. I have not tried to install it yet or even read a lot about it. It does seem have some administrative overhead.