I wish to upgrade to v7 asap. Currently using v6.5.5.

I understand I need to setup a new forums etc and import data etc.

Which version of v7 do I use to install the new forums?

ie your download list lists 7.5.6p2 and 7.5.6 as the last files. do both of these need to be used? Or an earlier update first?

Thanks.

From memory you need to install v7.5.6pl. In a net new folder. Then use a importer to move the existing version 6 forum to it.
That I guess is a good point since it is so old. Meaning if you have issues the original forum is still intact.

7.5.6p2 is the latest release, don't even bother grabbing 7.5.6