I heard they may have forgotten to retract the landing gear as well, can't have helped the glide range...
Dug up this while thinking about this incident. Maybe some similarities WRT to airspeed management, might not be...
https://www.atsb.gov.au/media/4931726/199601101.pdf
Best glide with both feathered would probably be close to blue line, would definitely not be a high speed with that airframe. Blue line would be at least close and safe to use. I know in heavier props recommended glide is just north of V2 type speeds. Haven't flown a BN2 so have no idea if there's a listed glide speed.