If nobody has visited in awhile the first visit takes a bit due to all the cached data needing to be rebuilt. I'm working on a couple ways around this, like possibly being able to setup a cronjob for those that can run php from cgi to trigger the cache rebuilds.
For now it's always a good idea to stagger how long things are cached for. Like some things every 2 minutes, some every 3 minutes, ettc.
Do you have a link to your test forums so I can see which options you have enabled. I'd like to see on a larger forum which ones are taking the longest. You can PM me the site if you don't want to post it for the public.
