Hi Mary,
On a 10ft wide boat the center of gravity of the boat platform is 5ft from the leeward hull center of bouyancy. This is 9 inches further to windward from the leeward hull than on an 8.5ft wide boat as you said. Moving the mast 9 inches to windward won't quite compensate for the 8.5ft vs 10ft wide boat difference because you are moving only the mast and not the center of gravity of the whole boat. In the case of the Tornado, for example, you are moving only 60 pounds of mast and sails and rigging weight to windward 9 inches. The boat weighs 375 pounds, so you need to move 375 pounds to windward 9 inches to make an 8.5ft wide platform have the same platform righting moment as a 10ft wide boat. Now on top of this we have the trapezing righting moment difference between an 8.5ft and a 10ft wide boat to make up for. This can be done with wings. The windward and leeward wings do not offset each other in righting moment. The windward wing has the full width of the boat, i.e. 8.5ft as its lever arm to hike with and the leeward wing has only the width of the wing, i.e. 18 inches to generate negative righting moment with.
Wide boats have no advantage in light winds. If anything there is a disadvantage because the wide boat is heavier. The wide boat also has to be built stronger than a narrow boat because the forces are greater on a wide boat. That is what makes the wide boat go faster in the first place. It gets more push out of the sails but only when the wind blows hard. I hope this helps.
Bill