What else
As a basic and general rule, if the engine will turn max. RPM, the prop is correct. If the engine will turn more RPM than it's rated max, the prop does not have enough pitch. If the engine will not turn up the max rated RPM, the prop has too much. But all these depend on the bottom and the prop being clean and in good condition. I also sail an S37. Engine is a 3GM 20. Three bladed prop. It will turn up 3400 RPM at max throttle. Cruise for me is between 6 and 7 knots at 2600 to 2800 RPM. A dirty bottom, a prop full of barnacles and any other problems on the underside of the boat can have a great effect on performance.