I am just under 100kg and for my sins living in a light wind area. I have tried many 85 wide slalom boards, most of the 90 and 90+ wide boards. With 9.5 to 10m sails, no question that the wider boards have a significant advantage in marginal winds. Boards like the latest Ultrasonic and Exocet RS7 don't give up anything in speed to the 85 wide boards in my opinion in the wind range we are talking about. The current Ultrasonic rides like a full on slalom board. The bigger fin it carries allows a real advantage in that it can out point smaller boards when needed.
It's rough where I sail for the light wind and I can confirm that the Ultrasonic really does sail fast in such chop(much better than the original Ultrasonic) Its footstraps are also better placed on the rail.
I think its a no brainer for larger guys to sail these boards in 8-12 knot wind slalom. Too many slalom events compromised by cancelled heats, marginal wind. No event = no more sponsorship.
Easy to say, hold events only where its windy, but the PWA has to be reactive and sail where sponsors come up with the funds, otherwise the tour will just fade away, which no one wants