Hi John!
Welcome to the Forum.
Your question goes to the root of what many of us have asked ourselves when choosing from Thorn's wide selection of offerings -- "Which one is best for *me*?"
Having owned a Sherpa Mk2 (essentially the same frame as a Raven Tour [RT] but with derailleurs instead of Rohloff) and now a Nomad Mk2 (essentially the same as Vendor Tom's father's on offer) I can make some comparisons.
I found the Sherpa to be a wonderful all-'round touring bike with ability to carry heavier loads -- say, up to about 33kg. I had a 560S (short top tube intended for drop handlebars) with the extra-oversize tubing with conical top and downtubes and found the bike to be very resilient, remarkably shock-absorbing, and pleasant for riding 200-300km/day on everything from pavement to singletrack. I used 26x2.0 Schwalbe Dureme tires on it and found them to nicely match the all-'round character of the bike. Briefly fitting 26x1.5 road slicks transformed the bike with a much sportier feel (reduced rotating weight aided acceleration and a lower profile changed the geometry a bit) and biased it more firmly toward road use.
Riding unladen, Sherpa felt much like my 700C-wheeled conventional touring bikes, but "more" -- I'd call it a heavy-duty tourer that also worked well as a day-rider and for conventional touring and general riding. Again, a terrific all-'rounder.
In contrast, the Nomad is like Sherpa (or an RT) but "more yet" -- a super-duty touring bike, capable of carrying the heaviest loads and biased more toward that purpose. The frame is thicker-walled and larger in diameter and so the frame itself is less resilient when unladen, depending more on wide/fat tires run at low pressures for comfort when riding without a load. My 590M Nomad is heavier at 20kg compared to about 18kg for the similarly equipped Sherpa and 14.5kg for my standard tourers, but an appropriate weight for a super-duty expedition tourer that will haul full gear plus extra food stores and 26.5l of water when needed. It is just exactly what I need and want for my extended desert crossings. The bike is still an all'-rounder, but biased firmly toward the "heavy lifting" end of the spectrum in my opinion -- ideal for expedition touring and a bit less so if most use will be day-riding unladen, as it really comes into its own when hauling a lot of cargo as well as rider. That said, I've enjoyed riding it unladen or with just a handlebar bag or rack pack. It did very nicely on a 200km mixed ride on pavement and logging roads in mountainous terrain, but required much lower tire pressures than Sherpa for comfort 'cos the Nomad's frame is stiffer.
Things have changed a bit with Thorn's redesign of the Sherpa Mk3 and merging of the Raven Sport Tour and Raven Tour into one offering, now called the Thorn Raven. The Sherpa Mk3 and Raven frames are identical except for the drivetrain. Unlike on the older frames, the tubing diameter is now proportional to frame size, and while ultimate cargo capacity is less, the bikes are probably better suited to riding unladen or with lighter loads in terms of comfort. In other words, they're probably even better suited to all-'round use than before. In contrast, the Nomad remains the dedicated expedition touring bike in the line and the one to get if you need to carry 50kg loads as I sometimes do.
So, I would suggest evaluating your needs (as you've nicely done) and use that list of requirements to select the bike best suited to the majority of your riding. All Thorn's bikes have a versatility of range and purpose far beyond that of their rivals and even their lighter bikes have some luggage-carrying capacity. Certainly, the Raven Tour (like the Sherpa Mk2) has successfully completed any number of 'round-the-world tours with no problem at all, so you wouldn't be limiting yourself compared to a Nomad Mk2 unless you have extreme carriage needs.
As much as I love my Nomad Mk2, in looking at your needs and requirements I would suggest the Raven Tour is better suited for your intended purpose. You surely wouldn't go wrong with the Nomad and many happily use it as their sole daily ride, but I think it is likely more bike than would be ideal, and its super-duty capacity might be a bit specialized for your general needs use, costing you a bit in comfort when unladen or lightly loaded.
That said, the Nomad and Raven Tour differ in their Rohloff shifter routing. The Nomad has an external shiftbox that attaches to the left side of the hub and conveniently removes for wheel changes. The Raven uses an internal cabling with two quick-release attachments. In actual use, they are equivalent for all practical purposes and I wouldn't let either be a determining factor in making my choice.
On either bike, a shorter top tube is better suited for use with the longer forward reach of drop handlebars, while the longer frames are usually paired with straight or comfort handlebars used with or without bar-ends.
As for the ability to easily manage steep climbs, that depends more on gearing selection than the overall bike. Since both the bikes you are considering have Rohloff drivetrains, fitting something like Rohloff's newly approved 36x17t gearing combo will get you up nearly anything regardless of load; many people are very happy with a 38x16t. Such changes require only a new chainring and/or cog and a shortened chain. Cost is minimal; I went from a 40x17 to a 36x17 for only USD$22 out of pocket for a new 'ring.
I hope this helps. If you have any questions moving forward, feel free to give a shout and I'm sure we'll all do our best to help. We'll each have our opinions and preferences, and taking the collective pulse will help answer the larger questions in making your selection.
Best,
Dan.
