Well for me and the forum we run we are very happy with vbull 4 and the upgrade from our 3.8.4 board which was very heavy in terms of mods in fact 50 plus were installed,went smooth as we were helped in the process by TheLastSuperman!!(
might be worth speaking with him if you are thinking about having someone do your upgrade)
Mike aka TheLastSuperman has some great info here on upgrading and makes a worthwhile read for any doing the upgrade!
https://vborg.vbsupport.ru/showthread.php?t=227933
http://www.vbulletin.com/forum/showthread.php?335689-