[TheLastSuperman]

Don't forget that 5 is getting better with time, like I've said before 4.x is running smooth at the moment so simply purchase a 5 license, install 4.x then upgrade to 5.x when its also running smoothly and done no worries, no stress*.

*Disclaimer: (WHAT?! lol) If you go crazy installing mods and tons of styles then yes when you upgrade to 5.x, if those said mods and styles do not have 5.x versions available they will not carry over and will need to be updated which may cost you money to have done although at this point in time the number of free and paid third-party modifications available for 5.x is not comparable to that of 4.x so there could be issues "carrying over" 4.x to 5.x mods regardless therefor running vBulletin 4.x for quite a while might be your best option at this point in time.