The advantages of 5/6 bladed propellers become evident at higher speeds. The disadvantages are evident at lower speeds.
The low speed disadvantage arises from the prop tip vortices, and their associated drag, which absorb some of the engine power. A 6 bladed prop will have twice as much loss from vortices as a 4 bladed one.
At higher speeds, where the prop tip speed is a trigonometrical function of TAS and propeller RPM, the prop tip reaches Mcrit, and propeller drag increases rapidly thereafter. From a performance aspect, this will limit the cruise speed available, and from a limitations aspect, will impose a lower Vno/Vne on the aircraft. If now, the same blade area is to be maintained (in order to absorb all of the power), increasing the number of blades will either allow for a lower propeller radius, a lower prop RPM, or both. Either will reduce the propeller tip speed, allowing higher cruise speeds and Vne/Vno before the prop tips become trans-sonic.
If the increase in number of propeller blades is also accompanied by an increase in blade area, the propeller will operate at a lower pitch/blade angle for the same power delivered. As Torque is proportional to the Sine of the blade angle, and Thrust is proportional to the Cosine of the blade angle, less available power is lost to Torque, and more is available for useful Thrust.
Advantages of a high wing? - Better view outside for the passengers, much increased lateral stability (perhaps too much), less damage to the airframe in the event of a wheels-up landing (particularly if the aircraft has a strong keel beam a la F27), offset by you being underwater in the event of a ditching.
Regards,
Old Smokey