Foxmoth
"600kts gives 10 miles/minute not 6 seconds/mile"
Surely 10 miles/minute & 6 seconds/mile amount to the same. The point you missed was "you don't spot him until three". Hence 18 secs to oblivion.
RTFQ
Mariner,
Best endurance is the bottom of the drag curve, so best range in a tailwind will be between best endurance speed and the 'still air' best range speed.