I would start with looking at the page source, removing frills, whistles and pop-ups. For example:
o- Fonts are discussed in another thread. The font chooser is useless and I’m not sure if external fonts are needed.
o- Autolinks are also discussed in another thread and also should be removed. (done)
o- Disable most pop-ups on mouse hover (topic content, open forum toolset, last message excerpt, etc)
o- Avatars must not be expanded beyond their real dimensions
o- Is “Thumbs Up/Down” system needed? There is the “Thanks” one already, which is more useful
o- Is “Print this post” needed?
o- Does “Mark as answer” change anything or give useful (and reliable) information? What if there are more suitable answers? But only one can be marked as “Answer”.
o- Is AudioPlayer needed (on each and every page)?
o- “New/Edited post saved” messages with slow fading effects are useless.
o- Do you know that the element has 11 classes assigned to it? Isn’t it a bit an overkill?
o- Define an extended cache validity time for static resources
o- Allow compression
o- It’s not just about the forum, but also about the rest of the site (e.g. WordPress plugins)
Just like in audio, all these small things, while looking small and unimportant have a substantial cumulative effect.
Web-performance sites, like http://gtmetrix.com, http://webpagetest.org/ and Google page tests give very good advices where to look at.