Courious to say that for me Roger was a little bit pessimistic.
I'm 90 kg (wannabe 85) and when I go windsurfing (outside Venice) after checking with the windmeter the average wind I do this way:
-11-12 ktn and more 8,0;
-15+ knots 6,5-6,3 sqm;
- 20+ knots 5,5-5,3 sqm,
- 25+ knots 4,5 sqm;
- 30-35+ ktnots: "hey Nico think about it you have cervical spinal problems so stay on the beach and admire younger and more skilled surfer, leave the 3,7 in the car". .
I use (and abuse) mainly Score 98 and Score 112, so the bigger but obviously little heavier Go could require little bigger sail, but also can handle lot more wind; and then imho I agree with the suggestions of Roger.