I ride a SUP but a very small one, considered a short board for a SUP. 8'2" x 28" wide JP Australia Surf Pro Edition (Thruster). I used the FCS online fin finder but it pointed to FCS II Matt Biolos. My board is FCS 1. So I emailed FCS to ask them if there was a fin very close to the Matt B. They said I would probably like the ARC. They gave me the dimensions and I purchased the smalls since I prefer small fins and I weigh 135 lbs. I have only used the fins twice, both in shoulder to occasional head high waves in clean offshore-wind conditions. One day was strong wind 15 kts, the other day was 5 kts to almost glass cond. I love the fins so far. I wish the top end was a little faster when wave is a fast closeout as I had some that were faster but not as controllable as the ARCs. Other than the speed though, the ARC drops into late steep drops with much more control and still plenty of speed with great hold through aggressive turns. I am a top-to-bottom type surfer and like aggressive turns that I can push hard on without loosing control, but with a little more push the fins slide controllably sideways for a tail-slide, then engages again with control. I do tight pivot turns and surf with speed and these fins go rail-to-rail smoothly. Thank you FCS!!