RE: Kombat 86 with very small sails ....
I haven't had time to try my Kombat 87 with smaller sails than 5.0 yet, but I've used it with Drake Natural fins from 22 to 25cm. The 22 works fine with the board and should work good with a 4.0 (I've sailed this fin on other boards with a 3.5 without problems - the Drake naturals have an amazing range). Since the Drake Naturals sail small for their depth, I would go smaller (21) if I would use a more traditional wave fin with a 4.0. At 85 kilos, a Natural 23 or other 21.5-22 should workk OK too.