I am very happy with the changes and the system response time. I don't think the who browsing the thread and forum feature will be coming back anytime soon, we are too big now for that feature.
When that feature was on for every page that was loaded the system needed to recalculate where everyone was on the forum, with over 1,400 people online and people constantly loading pages it was recalulating that information many times a second.
Looking at our SQL stats by turning those features off we went from 293 queries a second down to 43 queries a second. (Quite a savings!) This I feel is a big reason why the system is much faster as it is no longer trying to figure out where everyone is on the site.
This weekend I plan to update the site to vBulletin 3.54 which should offer us a few more improvements.
Whats funny since making this changes the memory usage has DROPPED greatly, we have 8 gig of RAM in our server and at our busiest times our memory usage is only 3 gig, meaning we have LOTS of room to grow. Also our CPU / Server locad has dropped from around a 1.1 down to 0.33.
I feel this was a worthwile modification.