I know the op asked for non steel suggestions
Spa do a disk steel
https://www.spacycles.co.uk/m1b0s225p3866/SPA-CYCLES-Wayfareror the standard touring canti. which I have with Tektro CR720 Cantis
it can take 37mm with mudguards
I have to say that the paint quality is excellent.
"All Spa Cycles branded frame and forks are ED Coated.
(ED stands for Electrophoretic Deposition. For steel frame bicycles, what this means is that the conductive steel frame and fork are placed in an liquid that has paint particles suspended in it. The bath is put under the influence of an electric field, and the paint particles are attracted to the charged frame and fork. The particles are fused to the frame and fork in a perfectly uniform thickness. The thickness of the coating can be adjusted based on the strength of the electric field.)"
The frame is really confidence inspiring, even fully loaded, on what the pundits call * technical descents*
And you can peel the decals off and add you own.
Or of course go for one of the Spa Ti Frames for and extra £900 or so.
Or the standard Audax frame in Ti or steel but the panniers may be behind the rear axle
PM me for pics as I dont know how to post images on the forum.
As well as my summer touring frame, it's become my main winter bike.
As I can change the wheels and tyres with no fuss.. dyno, 25s, 28s or Clémant MSO 32s Vitorria randonneur 37s.
I hope this helps