Hi Rob,
I hate to tell you this but we haven't tweaked a thing. Our vBulletin setup was tweaked like crazy to handle the traffic. Our xenforo installation is running on a plain jane CentOS setup.
Have you identified what's bringing your server down? Is it I/O? Mysql? Memory?
After running vBulletin for years on different sized servers on a big board site (which I sold), I have a pretty good idea on how it would behave under certain user load conditions.
I'm a new xenforo admin with a new site - and I'm really impressed with it's ability to handle big surges in...