Hang a minute Al, don't get it into your head that the Catalyst's fragile! It looks to be a great bike and I'm still debating the choice myself. I just fancy a Nomad as it has both V and Disc brake mounts, routing for the external gear box (which I already have anyway), S&S couplings that might prove useful (and certainly look rather nice!) and the ability to carry shedloads if I need it to.
DEFINTELY get in touch with SJSC and maybe even Andy Blance (the Thorn designer, who's very helpful) to discuss specifics rather than just listen to the denizens of the forums (although Stutho has been doing this for a while... [

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Also, if the weight limit on the Catalyst really is 20kg (and I tried and failed to find where it says that's the limit on-road, though 12kg off-road is stated) decide if you will be carrying 20kg. 20kg is a heck of a lot, even carrying an excess. Using a front rack as well, as can be fitted to suspension forks, would mean you could carry quite a bit more than 20kg.
As Stutho wisely points out, do as much of your own research as you feel you need to. It's easy to rely on the forums, and they're great for real-world user feedback, but go to the original source for advice on the right bike for you.
Oh, and hold out for matte green! I'm definitely going to wait as it's beautiful [

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Your trip sounds like an adventure and a half! Mine was, for the most part, considerably more tame. My girlfriend at the time and I took an overnight train from London to Inverness (it was great to wake up in the highlands!) and headed North up the coast and then North West towards Cape Wrath. I decided to give John O' Groats a wide berth as I'd been there when I was younger and remember being underwhelmed by the fog...
Anyway, it sounds like we made the same mistake as you which was to head back down the Western side of Northern Scotland - directly into the prevailing wind! The slog in the driving rain from Durness to Scourie was extremely miserable... Our trip was quite tame in that we were on road and using campsites (hot showers!) but the isolation up there was wonderful. Just the occasional Dutch caravan spoiled the peace.
The greatest skill the trip taught me was that you can imitate a sheep at one end of a field and it will spread a chorus of "Baaaaaa!"s throughout the whole flock! Heh heh heh.