vBulletin owns UBB 5.4
It's not all that big of a learning curve from UBB 5.4 to vBulletin. There are a lot more features to choose from, but there's little doubt they're probably going to strip it bare (e.g. no thread view counts, tiny avatars, no custom titles, no private messages, no attachments, no vB code, very few smilies, no who's online, no Currently Active Users, no members list, and a limited search) just as they did on Sharky's