Our forum has over 13 milion posts and 600-800 users online. We are considering migration from vBulletin 4.1 to XenForo. Actually we're happy with the performance of vBulletin on our setup: nginx+ php-fpm + xcache + sphinx search. However what we don't like is the direction in which vBulletin 5 is heading and XenForo looks like a nice alternative.
The question towards previous vB admins: does XenForo work faster or equally fast as vB on the same hardware setup? Does it scale for larger forums?