jack , obviuosly two big advantages to three blades -straight from the manufacturer
1)more ground clearance
2)less vibration

I have seen 4 differant websites when asking for prop suggestions , they all have differant data -not extremely differant but differant

I like the www.radicalworks.com propeller because they give you a starting prop -then suggest alterative props .

so for example -for a 4 stroke -2 bladed prop .90 size engine the range is
14/6 to start
then 13/6 14/8 15/6 16/6 is the range based on plane and RPMs -all listed on the site