I may get banned from the forum for saying this...
but at 19 stone and six foot five, I bought a Surly Long Haul Trucker because it has a 25 stone weight limit. It may not be as quick a bike as you want, but it rides really nicely and does everything I want it to.
Jim
My 58cm Surly LHT frame is only 200g heavier than my 56cm CT 4 frame. The Surly is as quick as the rider, I find it as quick as the CT 4 frame. Most of the 'quickness' of a bike is in the components, not the frame. The components that come on a new LHT/Disc Trucker are much better than those spec'd on the CT. The Surly goes everywhere, including loaded rides off-road. My LHT was derided by a roadie group, until I out sprinted their carbon-whatnots up a climb.
When I was buying the CT, and considering the Audax 3, I was told that the Audax shouldn't be ridden on anything worse than a smooth canal tow path (with no luggage). This kind of went against everything I thought I knew about steel bikes; in that they were pretty tough. But then, over the past year, as I've ridden the CT and compared it against my own experiences with the Surly, I've come to the conclusion that 'versatility' is viewed by Thorn and Thorn enthusiasts as a negative characteristic.
I love the fact that I cycled up Ventoux on TdF day, full loaded, and I'm cycling past weight-weenies in full Rapha clothing. The value of my LHT is in it's versatility, a week prior I was crossing from Spain into France on an off-road trail. I think this is the cultural fork in the road, where you take a left to Surly-ville, or right onto the road that values specialisation.
Certainly, if you promote/foster the idea of specialisation you sell more bikes. Owners of multiple bikes feel good, at having the right tool for the job (I guess). This is my bike for smooth roads, if I want to ride a canal path I take this one, off-road is this one, cloudy days I take this other one. The crazyness of 'gravel bikes' highlights this perfectly; it's a CX bike with new stickers, and a CX bike is a touring bike with new stickers.
A sherpa seems complete overkill/over-specialisation, just to be able to carry 15kg. 15kg! Get yourself a cheap mountian bike, or a second hand cheap mountain bike, and go and have fun. Use the £1000 you just saved to go on an adventure. I took a £200 Edinburgh Bicycle Cuillin mountain bike with 40kg of luggage on my first tour. Or just take your 853, I find it inconceivable that a steel bike would wilt with an extra 15kg on smooth roads.
I've realised that some people won't ever see the value of a LHT, because they've gone past that cultural fork in the road and are unwilling to backup a bit and question themselves. And when people compare Surly's to Ordinarys, Bromptons, etc, it simply betrays something about their cultural stubornness. Those sorts of people are not attacking Surlys or Bromptons, they're declaring their own loyalty to specialisation.
If you do a search for Joff Sommerfield, you'll find a pretty adventurous guy currently in Central America on his Ordinary, which he built himself. On this trip he's ridden down from Canana, and I think that sort of distance makes his bike 'versatile' and therefore of great value.
cheers,