My Naish is 73cm wide.
Widest WS board ever owned was 68.
155 lbs.
If I were going to windfoil, I would start with close to 91 wide so Ixd have the security and stability to sail in breezes of 1+ to get TO and FROM the wind line. Wind often drops, but sometimes the wind swells stay around and sometimes you get refraction chop. A wide board brings you home, but just as important, it allows you to go out in marginal conditions.
I see foilers on 91 cm boards foil in winds around 27 mph and have no problems with board size.
At those gusts, I'm fully powered with 4.5 and 85 liter ws boards.
I also see no gain in these 115 or smaller boards, because none of us a freestyling.