From the site I get m40c Tohatsu 1.92. With 14p propeller I reached 44mph. measured by GPS

http://www.tohatsu.co.jp/en/boat/products/m40csp.html

According to data from the site at 10% slip out that the engine speed is 7200rpm to 44mph. Even if it reached 60mph, I suppose 55mph is no problem with the propeller 19p. I do not know whether it is healthy for the engine.