Originally Posted by DiegoFrogs

Thanks for all of that!
My Centurion is ~ 14.0 mm in the plane of the bike near the dropout, 13.8 mm laterally... so it's tapering the full length of the blades. All the radii, tapers and transitions are gentle, which is visually appealing. Elegant, and a bike built to carry a load.
The Carlton is ~10.9 mm round near the dropout, and appears to have necked down to that diameter long up the blades. That bike also has rapid taper R531 chainstays without the normal crimps and kinks one employs otherwise. That was normally what I mentally considered as the magic potion, but I may have been wrong...

Thanks to everyone for contributing good stuff!