After a few days to recover from the lack of sleep...
The beds on the Mk5s are quite comfortable. The bedding was actually possibly better than that provided on the Riviera. Also, having the option to book a room with an ensuite is a very welcome change from the Riviera, where the Mk3s do not have any ensuites available. I'd booked a club rate sharing with a different family member, seeing as we're likely to only do this once.
The killer, however, is the horrendous ride quality. I don't think I've had a bumpier ride on a railway in my life, than I did on the Cally (and bear in mind I've done some heritage lines over some properly rough bits of track at, ahem, "25 miles an hour wink wink". The Mk5s ride diabolically poorly, to the point where I kept being jolted awake and hearing "dun-dun, dun-dun" at pretty much every station, every junction, practically every piece of pointwork. It boggles the mind that a comparatively ancient Mk3 can somehow ride far better than a more modern coach does. I am not a light sleeper, not by any stretch, and even for me it was a struggle to stay asleep.
Breakfast in the morning was a much better affair than what I had on the other sleeper. Getting a proper hot-cooked breakfast on a plate is certainly a step up from a sausage bap served in a bag!
I think Cally should try and arrange for some form of lounge sharing at Birmingham International. It's an important stop that they were very excited about adding, but it could be so much more. Providing lounge access at BHI would be very welcome considering the extremely early arrival time into Brum.
Finally, I'm not sure what happened, but I awoke to discover that we were running over 45 minutes late, having apparently lost nearly 50 minutes in Edinburgh.
All in all, it was an interesting experience, but I much preferred the Riviera over the Cally. It's just a shame that I have no real reason to go to Cornwall regularly, whereas I have much more reason to go to Scotland.