Thankyou for the thoughtful replies.
I am increasingly heading towards the Pass Hunter. Aside from anything else, it comes with a very nice build kit, most of which I'd be wanting anyway.
Regarding the choice of tubing, I am 210 lb and very strong. I easily flex the beefy LHT if I lower my cadence, even seated. So the regular 4130 in the Pass Hunter sounds like a better choice, based on what you've told me.
Also, regarding the 650B thing, my experiments over the years convince me that 35mm is nice for the sort of riding I do. I feel no burning urge to go above that. Also, I already have some rather nice 700C wheels that I haven't worn out yet.
I am beginning to understand that luggage is a very personal thing. I don't like how my Surly handles with an Ortlieb handlebar bag, but it is mounted very high and forward of the steering axis (owing to butterfly bars and a long stem on the touring rig). I might try a small front rack and rando bag on that to see how I find it.