Correct answer is... 760 km/h. It is equal to 410 kn or 472 mph. It is higher value then max speed of other aircrafts of a similar size. Average is about 268 km/h (145 kn or 167 mph).
The maximum speed most frequently is a term for so-called never exceed speed. Above this speed, the Messerschmitt Me 609 can suffer considerable damage. There are also three other types of speed that can be called "maximum speed": Vno (normal operation speed) is the maximum allowable speed of normal operation, Vb (design speed for maximum gust intensity) is the maximum speed in rough air, and Va (design maneuvering speed) is the maximum speed at which the rudders can be maximally deflected.
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