Considering you're weight and the sail sizes you're using, I think you could easily use the 82 as you're light wind board, but this depends upon whether you want the full on wave shape or the free wave shape of the 87. I sail my K86 mostly as a B/J board and high speed cruiser when the wind is +18 knots. It is one of my favorite all time boards for those conditions. Mostly used with a 5.8-5.4. I'm 84 kg.