AlanK: I hear you re. Thorn; I'm just a real sucker for their overall design (which does come from a great deal of experience), and (a shameful admission) their promo. literature -- oh, those pictures of expedition tours in far-off lands

I have a dream (prolly completely silly at age 57) to do the Argentina/Patagonia thing -- oh well!
Back to reality, I agree completely re. Spec/RM etc., especially wheels. I do think one is stuck facing a few upgrades if going this route. The Jamis I'm familiar with -- my much-loved LBS is a Jamis dealer. They really are excellent bikes at their various price points; on the Durango, I would say go for it, but I do think you will be replacing those hubs (Shim. 475). My Rainier came with them; I just don't think they're adequate to high-mileage riding. I rebuilt mine a couple times before saying 'h_ll with it' and going for XT. But then, I'm a bit of a fanatic when it comes to wheels. Other than that, would work well.
The Safari I know about, though have never seen one (don't think we can get them up here). Now, that does look like the kind of thing that would work extremely well, especially if you're not wedded to front suspension; lots of owners seem to love them. Suspension is in fact my last major decision; I did upgrade my Rainier's fork to a very good Marzocchi (MXPro), which works very well/is very reliable; this year will be my 'year of the carbon rigid fork' experiment, to see how I get on with a good rigid fork/wide tire combination over varying surfaces. Once that experiment is complete, my 'plan' is to have a frame built for me, with all the braze-ons etc. I want, and transfer everything over. I only own/want to own one bike, so feel justified in going this somewhat wacky but fun route

Edit: now that I think of it, maybe I can use that last statement as the foundation for an argument to order a Thorn -- oh dear, it's never-ending!