What if item/quest/mob/zone pages didn't load forum posts by default but provided a page link/button to load them on demand. That would decrease load if the posts weren't what the user wanted. It would also decrease load by splitting the forum post query off of the main query. I would assume decreasing the number of tables queried in any given procedure would show immediate benefits. Alternately you could modify any query to only retrieve posts from the last 5 years by default with an option to "load older posts".
Another idea: drop the post ratings from those pages. One less table to query, and weren't ratings on those pages disabled a while back anyway?
Another idea: delete sub-default posts and any replies to them. I know deleting posts isn't optimal but creating a more responsive site is pretty important.
Pretty sure that rating posts has a timeframe, once a post is "old" you can't rate it. But... it's possibly that some really old posts here may not follow that rule, and since I don't know how that rule was implemented (was it a manual thing that Fleven & Railus set the timeframe on?) it is even possible that it only applies to a body of posts from a specific static time period.
Deleting sub-default would be 85 or 98% effective... but that small percentage of old useful posts that got evilly downrated would then be gone. I have found (and corrected) a few instances of a person sharing information about a rare NPC or raid encounter that a few someones decided shouldn't be shared and rated the person down.
As an aside... the site doesn't even delete posts the admn have nuked. You (as a user) just can't see them. That would be my first step... if the post is admn nuked it is gone. Then as admn continue the regular updating of stuff they can keep weeding out sub defaults and useless posts like the still present 1000s of posts telling how a particular class deserves a low weight item whether its stats make sense for that class or not... (for example).
You touch upon a radical notion though... if the rating system is making the site slow
maybe we need to lose the ratings from everything but the general forums? Or even altogether? I know many of us worked pretty hard to earn our "colors" through the Karma system but there are quite a few low-post count people with high ratings that didn't. Could always grandfather the sages as green and gurus as red with the tag "veteran user" and just set all new users in scholar blue from now on? --I know that may sound odd coming from a person that heavily used the ratings system before ever becoming a volunteer admn, but in truth very few people that bother to login to the site use the ratings system for the last few years anyways --back when we had weekly update posts it got used a bit, but as far as good quest info or item info posts, almost no one rate them up for years here. Something to consider at least.