Ken,

The terms "cruising speed" and "top speed" are in fact relative terms. There is a theoretical concept called hull speed which is related to length of a boat. Longer boats have higher hull speeds. Speeds above hull speed can be achieved by a strong paddler. The effort required to maintain each increment above hull speed increases significantly as you are fighting your bow wave in addition to friction.

A more important factor in speed is the width and shape of the hull cross section. In general the narrower and more rounded shape results in less drag and a faster boat (i.e. the effort to maintain any given speed is less)

People looking at boats generally make tradeoffs to get a balance between speed, stability and maneuverability. You may prefer a somewhat slower boat to get some stability. You may choose a somewhat shorter boat that turns easier.

All things being equal (which they rarely are) a reasonably fit person in an average boat can cruse at 3-5MPH all day and can achieve top speeds of 6-8mph for short distances.

Olympic racer in super fast skinny racing boats can do a marathon at 8 mph and can sprint at 13mph

Regards,

Jack