I use an 80 cm mast, practical when you have to start at low water between the sandbanks, and then you can foil over the bank to the outside.
Still sufficiently long to be able to crank over in carves without getting the wing free.
But a 90 cm seems to be what many likes (I havent tried one wingfoiling, only for kitefoil where I prefer 92 or 100 cm).
There is one advantage in wingfoil though, as even if you get the wing too high, so it semi-ventilates, it does very often recover, as opposed to many kitefoil wings.
Also, you dont lean the foil over much when going upwind, so here a longer mast is not needed.
It would be when carving around hard, the difference would appear, or for control down bigger wavefaces.
I am also curious as to what others, who HAS tried different lengths, prefer