At least Baugher gives his sources:
Japanese Aircraft of the Pacific War, Rene J. Francillon, Naval Institute Press, 1979.
Famous Fighters of the Second World War, William Green, Doubleday, 1967.
Aircraft in Profile: The Kawasaki Ki-61 Hien, Rene J. Francillon, 1966.
War Planes of the Second World War, Fighters, Volume 3, William Green, Doubleday, 1964.
Book by Richard Bueschel called Kawasaki Ki-61 Hien in Japanese army air force service, gives max speed as 379 at 19,685 ft. and climb at 2734ft/min.
If I did the math any where close to correct. Climb is listed as 5,000 meters in 6 min.
That's the data for the later Ki-61-II.

Not like it matters, I suspect the plane as it will fly in AH won't quite match any of these numbers.
