I don't know how much experience GB has with the vB software or even databases for that matter, but it is a bit of a lengthy process, and I'm guessing we're still on 4 or maybe even 3. The most noticeable change for the end user would be better support for mobile devices and tablets.
https://www.vbulletin.com/docs/html/vb5_intro_whatsnew
Edit: Oh, ok. Nm.