Hats off to you for accomplishing this handheld. I've made nearly the same photo at a cathedral in Spain (
https://flic.kr/p/K2Gghh), with a Bronica S2, but not handheld. I propped the camera upon a pew, pointing straight up, and used a release cable. (There also exists an iPhone snap by my wife, from minutes later, showing me standing next to a large, multi-lingual "Quiet Please!" sign in said cathedral with the distinctly non-quiet Bronica.)
To the original question: I have a 'flex 2.8E, but I do not do much major travel with it. The Rollei inspires in me a bit of FOMO WRT wide-angle compositions, being limited to the fixed 80mm lens. With the Bronica, I carry the normal lens and a 50mm (and may some day get a 40mm) so I know I have the flexibility to shoot wide. The weight penalty is, obviously, substantial. As a lesser concern, also my 'flex is somewhat a family heirloom, and travel offers so many ways to have things lost or stolen. I by no means regard the Bronica as disposable, but it would not as much break my heart if it were lost, and it's cheaper to replace than the Rolleiflex.
--Dave
Believe it or not, I've done that with an RZ67, pointed straight up, no less...If it wasn't 1/8th, it was no faster than 1/15th. So it can be done, but you have to have rock-steady hands. Which apparently I do.