Back to RoD. Thanks, Shy-T.
PFL, engine at idle: some residual thrust, thus RoD less than if engine and prop stopped. Windmilling engine needs energy to turn it. OTTOMH, I think the drag would probably be greater than any thrust from the auto-rotating prop and thus RoD greater thna engine at idle.
Now my curiosity has been stirred, wonder if I can find anything in the books......