RE: free ride fin for 85L
Here's an idea: For more grip when shlogging / pointing without compromising high-wind control and turning ability you might try a short fin with lots of area. A "weed-wave" fin fits that description. Several brands of them are popular in the outer banks shops.
I have an Orca Weed Wave 25 cm that I really like on my 77 liter board in gusty conditions. One bonus is that since it can provide lateral resistance at lower speeds, you can slow down and point upwind in nuclear gusts without side-slipping.