The bogies don't tilt. The body profile allows up to 6 degrees of tilting. They were intended to to be retroftted with APT-derived bogies if a tilt mechanism was added later.
Yes, the CAF coaches for both ScotRail and TransPennine are designated the Mk 5.
Here's some thoughts on more fictional rollingstock.
Suppose the parcels and newspaper traffic had continued and there was a need for a more modern GUV.
Suppose the mail traffic had continued and the proposal to convert surplus Mk 3 sleepers into 125 mph Post Office storage vans had gone ahead. My understanding is they won't going to convert any to TPOs, just storage vans. The time saving from 125 mph running would have allowed mail to be sorted at the destination rather than en route. I'm guessing they would have used a DVT on these rather than build a new PCV.
Or for 100 mph parcel and newspaper trains, what about a PCV derived from a Mk 2 DBSO?
EDIT: Suppose milk and/or fish traffic had continued and there was a need for new passenger rated insulated vans, or even refrigerated vans powered by ETS.
Cheers
David