Hi there, any chance to test it? I mean the single fins do generally plane quite well, but then you need 2-3 fins and multiple boards to handle the range that a Quad can deliver. So I used to have 4 wakeboards on a trailor with 2 fins per board. Now I put my 82 inside the 4 door sedan when I'm in Cape Town and have 3.7-5.3 in every size, no extra set of fins...so it shows the range is certainly far greater than the older shapes.
You mention you'll have a 82 Grip, so you are anyway set for the lighter days, go for the Grip 68, great board for lighter riders.