Thanks crab, I am aware that your definition of lowest ROD is more orthodox as it refers to the maximum excess power which the "power available" curve has above the "power required" curve.
I threw in the disk attitude idea as a certain helicopter guru instructor at Maroochydore reckons that's a practical approximation to the lowest ROD airspeed in an auto.
Shawn, I understand that full down autos are not even part of the FAA CPL(H) syllabus and they generally don't learn those until they get to CFI stage. Thankfully I was trained here in Australia where we get to perform such varied manoeuvres as autos from 50' AGL as part of our CPL(H) course.