Congratulations to Rivendell for their survival.

My vintage bike is not suitable for a wide tire/rim option beyond 25/23, but for my new bike application, frame clearance and brake alteration considerations were off the table for the most part. The initial build began in traditional 700c style with 25 nominal tires (actual 24mm), progressed to a different 25 (actual 28mm) tire, and on to a much more comfortable 32 (actual 33mm+). The 32mm was an eye opener to comfort possibilities, and I wanted more, but reduced tight turn radius and increased overlap were trade-offs. Part of the overlap was from 175 crank arms, which were good for my standing climb style up to that point. Long crank arms also provided increased leverage required for the new 32's greater rolling diameter, so it was a shame the crank had to go. I could also see a fatter 700c tire would introduce less than ideal compromises; precarious top tube proximity being one of them.

For disc brakes, 26 inch is the first option I considered for tires beyond 32mm width. However, to attain a similar rolling diameter as a 700c/23 in a 26 road tire, the tire would be too wide for this frame's rear stays, and the tires in that size were very thick & heavy (puncture resistance is not one of my priorities). A consequence of reducing tire width in a 26 to provide frame clearance, thereby reducing rolling diameter, would mean no more pedaling while leaning over.

A 650b rim & 42mm tire would appear to satisfy most objective requirements, and it did, along with subjective wishes; top tube stand-over is preserved, maneuverability improved (partly due to rim selection), stability improved, and overlap eliminated. I found many reasons to think it would work for my application when other wheel sizes wouldn't. I'll go a step further and say, Grand Bois Hetre (42mm) tires are a good enough reason on their own to go 650b for road use.