[soniceffect]

From someone who has only just upgraded to 3.5.1 from the previous 3.5.0 .. Which is indeed a fix for security reasons as you have specified is half of your problem .. I can give you a basic idea ... My forum is 'hacked to high hell' all of which would have in previous versions php file edits ....

Previous versions - Estimated time to upgrade I would guess at a 2 - 3 hours, and I have a pretty good idea what I`m doin..

Current version that I upgraded from 3.5.0 to 3.5.1 along with hacks/mods ... 10 mins tops ...

If this is the reason you are thinking of upgrading to Vbulletin .. Then upgrade...

On top of this, as a former phpbb user and ibpro user, vbulletin (excuse my french) pi$$es all over them and makes them look like childrens toys... If you want power at your fingertips, excellent support from both staff and members here, plenty of mods, and the best bulletin board software, then purchase it .... Vbulletin is in my opinion, always an upgrade from any other system.

EDIT:- On the note of editing extentions .. This can also be done though the plugin system, as the plugins are simply php code that runs at a particular place within the vbulletin script, and is editable via the admin control panel.