No twin engined aircraft can climb with one propeller windmilling. You should know that instinctively!
Having more than a few hours C&T on the DH8, including the Simulator, I have witnessed, on several occasions, a twin engined aeroplane do just that.
A colleague with my current employer was also a colleague in a former life. He was flying a Nord out of Sydney for Tamworth when a blade separated from the 5 bladed prop, and in doing so damaged the hub preventing feathering of the prop. With a load of pax, they continued flight back to Sydney with the remnants of the prop windmilling happily.
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One must agree that Stallie's comment above is right on the money. Legal isn't necessarily best.