Well, there are plenty of people in the UK who bought without the visit to Bridgewater and you'll be hard pressed to find anything but a positive report of the experience. All the Thorn bikes have a vast range of frame sizes and by all accounts I've seen they can fit you perfectly into one of them as long as you give them the full information in the order form.
Like you, I like the Sport Tour more - or at least the brochure told me I did. Sporty, fun handling and the lure of the 853 steel. And that's what I bought. But as my cycling progressed from day rides to include touring, in some ways I've been struggling to stay within the weight criteria.
Elsewhere you'll see I've posted to say it's ok with the full 20kg and four panniers, and that's true, but there are times when I just say to myself, I wish I could pack my stuff in two big rear panniers and not worry. Or, there are things I leave behind because the handling will start to suffer a bit. On tour, I find a can easily come out of a shop with 2-3 kg of essential food and as I pedal off I can tell that the ride will improve when I've consumed some of it!
Certainly, if I wanted to do a big tour I think I'd do what beef suggests and equip a Nomad frame with all my RST components just for the absolute security and freedom of loading.
So, the common sense option may well be the Raven Tour (or Sherpa maybe), which I haven't ridden, but I understand is more stable with more weight.