I am going for a 70cm mast. It should give me 55 ish before the prop ventilates. It doesn’t sound very high but I think its high enough for this application.
Also from my experience kiting and surfing on foils, If Im kiting on my 70cm mast and breach the foil, about 50% of the time Ill recover without wiping out. On my 95cm mast its never!
I also think the power from the prop will be easier to control from a shorter mast. I think because the power is coming from the bottom of the mast, it is essentially a big lever on a fulcrum point (where it joins your board). The shorter the lever, the more control I will have with my weight up top.
These are just my thoughts and not based on efoil experience yet. My build hasn’t hit the water yet.