Actually the manual says 8.6K for 31 bhp at peak performance for the 360 and 7.6K for 33 bhp on the 400. The 600 had a 45 bhp or 42 bhp depending on the country importing the vehicle.
Many years of testing proved the RPM range given the Honda 600 sold in the USA had to come down.
The only High RPM vehicle sold to the USA was for Hawaii, and at that time Oahu didn't have a freeway. It is the freeway system the USA has that brought the detuning of the 600 to 36 hp from the 45 hp unit sold in Hawaii.
Even the vehicles sold in France and England only had 42 bhp. Leading us to a single point, a brighter candle burns twice as fast.
I believe it was Dean that said he could resleeve the cylinders, having a standard cylinder and piston will keep the heat down. Heat after all causes much of the wear on these engines. Cooling them down is going to only do so much. Driven long enough temperatures will rise and heat will be the result of failure.
Change your oil often and keep your engine clean.
Bill