Got some help by ChrisPurcell in tuning Oddmuse... It turns out that there was a way to save a lot of matching when handling smileys, and there was a way of calling extension rules that is faster than what I originally had.
You can use wiki?action=browse;id=pagename;cache=0;time=1 to measure how fast a page is rendered. On the CommunityWiki, the longest page is CanTheSemanticWebWork and rendering that page took longer than the 90s allowed by the hosting company... :_ With version 1.422 in place, however, it takes 8s! 😄_
​#Wikis