Prop questions for Rotax

I am getting ready to replace the prop on my Rotax 582 with 3:1 ratio. IVOProp told me that I could only use a 3 blade prop if I change the gears and the prop I want is a 3 blade ultralight prop. Here is what IVOProp told me about 3 blades and 3:1 trannys;

Rotax 503, 532, 582, 583, 618 with 3:1, 3.47:1, 4:1 gear
ratios or other similar engines with high reduction ratios.
Recommendation is the meDium propeller with 5.5 inch diameter
hub. We can no longer recommend the Ultriaght model propeller
because of harmonics associated with these higher ratios
causing blades to move in the 4 inch diameter hub in the
direction of rotation indicated by the motion detector
tape that cannot be stopped with the torque value.
We no longer give refund or credit for undamaged
parts with Ultralight model on these combinations.

So my question is based on the fact that I do not have my head wrapped around prop dynamics. What would be better, a 3 blade ultralight prop or a 2 blade medium? Based on what I have heard I could probably run 70-72" on either setup with difference being 2 thick blades or 3 thin. Anyone have some science or math they can throw at this question?