Hi Phil!
What a wonderful dilemma...it's always fun to bike-shop and see what's "out there" when contemplating a new purchase.
Putting in my two cents' worth...
My 1983/94 Centurion Pro Tour rando bike has front and rear pannier racks, does well touring with about 40-odd pounds/18kg of gear, and uses 700x32C road slicks on Mavic MA-2 rims with 15g spokes. It was my main touring bike for many years, and is very close to the Club Tour in basic spec (uses standard road-diameter Tange Champion No. 2 frame tubing). Weighs right at 32lb/14.5kg and I regularly ride it on 300-400k day rides including gravel logging roads -- loaded and not. I think of it as my all-'rounder, and I can't imagine better for my general needs. Again, very close to the Club Tour's spec and mission as a "traditional" tourer.
In comparison, my Sherpa Mk2 rode very similarly, but was "more" bike in terms of having a larger-diameter, sturdier frame and a lot more weight in my chosen wheels (Rigida Andra rims and 2.0 Schwalbe Duremes -- a brief change to 1.5 skinwall unbelted slicks made it feel like I had turbocharged it, but at the expense of ride quality). Overall, it weighed 10lb/3kg more than the Blue Cent. It, too, was a great all-'rounder, but at the "heavier-duty" end of the spectrum. I had it setup with drop handlebars, and configured that way, I think it would be fair to describe it as a "super-duty" touring bike in feel and mission. It was pleasant at all speeds, but did not feel as lively as my Blue Cent but did far better at the more rugged end of things. A good part of this was due to the frame, and a good part was due to the tires. I think the frame made a bigger difference when touring with a load, and the tires made a bigger difference when riding unladen.
Tires and wheels make a huge difference to the feel of any frame, especially when riding unladen.
With the introduction of the Sherpa Mk3, the gap between it and the Club Tour has narrowed a bit. Though I have not ridden one, looking at the brochure and specs and depending on frame size, I think a Sherpa Mk3 with Rigida Grizzly rims and 1.5 or light 1.75 tires would come very close in feel to a Club Tour running wide 700C tires on heavyish rims -- especially when ridden unladen. The Sherpa Mk3 has a reduced load capacity compared to the old Mk2 due to smaller tubes. Some has been returned through the use of a fork with heavier SuperTourist blades that allow a greater load up front, but the frame itself has a bit less orientation toward expedition touring.
With all the above in mind, I would say if you plan to do a lot of loaded touring on poor roads, then the Sherpa Mk3 with Grizzly rims might better suit your needs due to available tire choice. You could always go with lighter, narrower tires to make it feel more lively when riding unladen (they may not have less rolling resistance, but they do accelerate faster and so "feel" quicker).
If most of your riding will be with moderate loads and a majority on paved roads and/or unladen, then the Club Tour would be a great choice.
If it is important to sometimes have tires wider than 2.125, then another bike entirely would be a better choice. Building on Ian's suggestion, how 'bout a Ripio...with a Mt. Turo fork? That could be the best of all worlds for your needs, and could always be fitted with lightish Grizzly rims and 1.75 tires for a good all-'rounder when not loaded touring. A simple tire swap would get you much of what you seek when touring in the rougher stuff, and the fat tires would go far toward protecting the lighter rims while allowing go-anywhere capability.
I hope this helps. Others will have excellent suggestions of their own for you to weigh. Please let us know as you refine your desires and hone-in on the "perfect" bike for you (and it will be, no doubt!).
All the best,
Dan.
