Hi Barry!
My, what exciting news, and I hope it all works out to the best for you!
Looking at the Thorn Nomad brochure, the tubing diameter is different between the standard and "X" models. Yes, the "X" has reduced carrying capacity compared to the regular Mk2 Nomad, but for general use, this will make for a livelier-feeling, 500g lighter bike and would be no detriment provided you did not need the Mk2's greater carrying capacity. It would still be suitable -- and more -- for the kinds of touring many people do.
The geometry of the "X" bikes varies as well, as shown on pages 20, 21, and 22 of the Thorn Nomad Mk2 brochure:
http://www.sjscycles.com/thornpdf/ThornRavenNomadBroHiRes.pdf In the text, Andy Blance notes, there are *four* frame sizes available in the "X" series, and they all have medium-length top tubes (pg. 20). Well worth a read for anyone interested in the "X" Nomads.
As for warranty transfer to a second owner, from all I can see, Thorn's applies to and covers only the original owner. Please see page 40 of the owner's manual, here:
http://www.thorncycles.co.uk/thornpdf/ThornBikeOwnerManual2Web.pdfAs for Rohloff's, if the little orange card registering the hub has not been sent in, you might try doing so. In any case, if the hub has been registered, you will wish to contact Rohloff so they can update their records. They're really good about keeping a database by owner/serial number to aid recovery in the event of theft.
Given the reliability and durability of Thorn's frames and the Rohloff hub, it is unlikely you would need to make a warranty claim, but that is always the Unknown. Every manufacturer has the potential for some unseen flaw, *but* these usually manifest quickly and early in ownership, so if the previous buyer has had a good experience so far and the bike rides well in your trial, then I think you could feel confident all would most likely be well. The difference between used and new in that case (assuming the bike was in very good condition and spec'd to your liking) would be the warranty -- in effect, an insurance policy you hope you wouldn't need to collect on.
I hope this helps. Very best of luck to you, Barry. Please let us know how things come out for you.
Best,
Dan. (..who thinks an "X" just might hit the mark for many people)