Ultimately we decided upon Nimbus hosting who so far have been excellent.
We now just need a little bit of help with setting up some nginx rewrite rules as previously we were using Apache, but these aren't as straight forward as normal rewrites.
At the same time we moved from vBulletin 4 to XenForo, we also changed our domain name from Halflife2.net to Valvetime.net.
We have two options:
A - We simply get help with rewrite rules that redirect http://www.halflife2.net/forums/* to http://www.valvetime.net/* and we let the VB4 redirect scripts (showthread.php etc) do the rest which is effectively two redirects.
B - We forget about the redirection scripts and we get help with all the rules necessary to redirect vB URLs to XenForo, e.g. http://www.halflife2.net/forums/showthread.php?t=12345 -> http://www.valvetime.net/threads/12345 etc.