As noted previously, our site has a large DB, so it runs quite slow on any 2.5 code (9-13 seconds main page load, with the addition of the akismet and b8 tables). I revisited the (three) worst performing queries on our site and seem to have found a good solution for each that makes performance (< 1 second main page load) close to 2.4.24.

/includes/main.inc.php queries:
total_spam
total_postings

/includes/index.inc.php
latest_postings

I'd be glad to share these with you if you're interested. I still have some testing to do to make sure I didn't break the code for different configurations than our own, but so far they look solid.

Joe