Good post mephisto!
I'd almost forgotten ULH in the classic. Three pilots and two engineers. It truly was as you put it. To achieve the FDP you had to burn out the relief so that the other two pilots got adequate rest to extend the duty. The relief's FDP began at sign-on and ended approx 12 hours later. He was in the seat for a max of eight hours at one time, rested for an hour then back in the seat to an overall max of ten and a half hours!
Excellent closing para as well!