So, to the fin quest for my JP 9'6 Surf (I weigh 88 kgs).

Tried the Shapers Jackson Close SUP fin set - it appears to have the S7 centre combined with S9 sides:



This makes the board less loose if anything. I think this is because the S9 sides are larger than the original M5s:



The Shapers S9s also have way less tip flex than the M5s. I am thinking this may be a disadvantage with the straight fin set up.

So, its back to the OEM as the board is nice and loose with that set up.