Hi, I just imported and switch my Forum last night from vBulletin 5.4.3 (the most terrible mistake to upgrade to VB5) to XenForo 2.0.1 using the official XenForo Importers 1.0.2 and all was straight forward.
Threads 376,480
Messages 4,873,846
Members 38,182
Took a total of 8 hours
I just had to tweak couple things, changing the DB char_set to utf8mb4.general_ci and change the old_id column lenght to char(150) in the new import_log table.
My users love it, specially with the speed, since VB5 it was just WAY TO SLOW.