I vote for increased length as long as it is less than 13 ft. So, 3.9m. The reasons are both selfish and practical. I am 5’11” 175lb (~ 1.8m 80kg) low body fat. If your calculations are correct, I defiantly would not build one to use for weeknight sails. Through design, we should be able to minimize the penalty incurred by smaller sailors. We can always make the smaller sailors’ boat smaller than the box. It would be nice to have the boat perform while we are taking are children out to learn.