Forgive my ignorance - but if I am understanding you all correctly, some of you got to in excess of FL60, with only the Taylor helmet and a pressure jerkin, relying on cockpit pressurisation alone?
So presumably, if the canopy had sprung a leak, or you'd had some kind of explosive decompression event, an emergency descent would be totally out of the question - you'd be unconscious or have boiled blood (or both) before you'd got anywhere near a safe altitude.
Young and brave indeed.
What was the maximum balls to the wall rate of descent for a PR.9 in an emergency?

This article dated 18 Nov 2019 from The Aviationist should interest the same audience and saves resurrecting an ancient U-2 thread.

We Tell You The Story Behind This Extremely Rare Two-Ship U-2 Dragon Lady Formation Flight

https://cimg0.ibsrv.net/gimg/pprune....765c95f7cf.jpg
A U-2 Dragon Lady flies over California at nearly 70,000 ft., Mar. 23, 2016.
U-2s are home based at the 9th Reconnaissance Wing, Beale Air Force Base, California.
(U.S. Air Force photo/Staff Sgt. Robert M. Trujillo)

AEA for high-level PR9 ops in latter days consisted of only the pressure jerkin and the g-suit. These were both fed by the output from the Mk 21 oxygen regulator which also fed the oxygen mask. The relatively high pressure feed to your mask was stopped from bursting your lungs by the equal pressure in the jerkin and g-suit! This would give protection to above 50,000ft.

AMTW training for the PR9 included a rapid decompression in the one-man chamber at Farnborough; 25,000ft up to 56,000ft! Not exactly comfortable but it would certainly allow you to stay conscious and keep flying the aircraft to initiate a descent. The latter was flown with full airbrake and open Flare Doors. Quite demanding handling in terms of pitch and very easy to over control. If you got too fast the aircraft's significant pitch-up was greater than any nose-down from the elevator which would clearly somewhat abate the descent rate.

From the BBCV
 

Interesting article here