Not quite clones
I lined up the midlifecrisismobile and the born-again Trek so I could compare the geometry of my low-trail 700c rando bike vs my medium-trail 650b rando bike.
The trek is noticably smaller; I’ve got easily 3cm more saddle to bar drop on it than the mlcm has. That, I suspect, is the largest benefit of 650b for me; I can ride a machine that doesn’t look like a folding bike, but still have enough breathing room for a comfortable saddle to bar drop and fenders (w/o a horrible case of toe overlap.)
I’m reaching the time of year where I can start to do comparisons between the trek and the mlcm, too; the rains are coming in so I’ll need to swap off machines depending on which one has fenders (at least until I lay up some carbon fiber fenders for the trek.) I’d say it’s unfortunate that there are so few good 650b tires out there, but aside from my dalliances in the tubular tire world the only 700c tire I’m using these days are Resist Nomads, which makes for fewer 700c tires than 650b tires (in 650b I’ve got Confreries, CdlVs, and Pari-Motos to play around with) in my collection of good tires.
And, yeah, the Trek has an excessive amount of carbon fiber on it now; it’s teetering on the edge of being under 22 pounds, which makes almost no difference in how fast I can ride on the thing, but which is very amusing in the “you have a front rack and leather saddle on what!?!” department.