I have a large vbulletin 3.8.x forum (Threads: 1,366,377, Posts: 20,663,439, Members: 302,724) and I'm starting to have server issues. I'm looking at upgrading the software and I'm kind of torn between Xenforo and vB5. I've got a few smaller forums running SMF but I've heard it's not as good as the others for larger forums. I've never used Invision so I'm not sure how viable it would be. Whatever software I go with I have a few concerns. I have a LOT of custom sub-forums, some set up to be invisible to everyone but a specific usergroup and password protected. I've got several unique usergroups with their own permissions. I've also got a two tiered paid member usergroup, one annual and one lifetime. Given the size and history with vB, I've been running it for over a decade, upgrading to vb5 seems like it would be the easiest however I've read a lot about how it's changed and isn't what it used to be. Xenforo looks nice and is from the same guys that made vB3 so it's got that going for it but I'm not sure how all my permissions, forums, passwords and such will transfer over. On the smaller forums I really like how clean and simple SMF is but there's that recurring suggestion that it's not suited for larger forums. I'm looking for input on which software would be good from people running a forum of similar size and the viability of each with a larger forum. Thanks.