Well, it's not so much "data", rather my informal observations. I did not gather this "data" with the normal flight test methods expected of me, so it's not really formal, but certainly add it to the collective wisdom any way it helps.
By the way, this exercise was done not so as to propose the purposefull stopping of the prop in flight, but instead, to see what one might expect if the engine seized. That did happen to a friend in his C 180, a long time ago. (force landed on lake safely).
By the way, shut down tests I have done in twins in the last while each showed that a windmill start is very hard to achieve. The DA 42 with MT props and Lycoming IO-360's would not windmill start at any speed up to near Vne. Changing pitch of the stopped prop helped a little, but not much. The Twin Comanche I tested with MT props the other week (would not unfeather)) had to be startered - and it was not nice!
In gliding a Caravan last month, I found the descent rate at flight idle was reduced by close to half by feathering the prop (engine running in flight idle). That perhaps has something to do with the rather "disking" characteristigs of the Caravan in fine pitch.