the best forum ive ever seen is Ultimate bullitin board, even though im an NT guy, and UBB runs in Perl.
The reason UBB is better than any CF or ASP forum i have found is simple, it writes each topic into static HTML, and only rewrites the topic when someone edits or posts to that topic. (if your on a modem youll notice when a topic loads in a fusetalk forum that each post comes up seperate, indicating the script loads that post, dumps it, loads another, dumps, etc., static HTML just dumps the whole page)
This is good for several reasons, first, static HTML will destroy any CF, ASP, JSP or whatever scripting language you use, no contest, servers can spit out static html like nobodys business. second, search engines prefer static pages, easier to index, thus more exposure there, if you want it anyways.
If fusetalk makes a forum which outputs static HTML, that would be awesome, but until then, UBB is tops in performance. I only wish they made it in ASP or CF