Originally Posted by Jean-Marc
For a 2 boards quiver with your 70kg, I'd go iSonic 86 Slim (5.5/6.0/6.6) and keep the iSonic 111 (6.6/7.3/8.0): plenty wide with 8.0 max sail for your weight (planing as of 10/11 knots).
Thank you all, and Jean-Marc in particular who is close to my weight.
Interesting observation about sail/fin as limiting factor. I have an old Mike Lab "boat" (ultralight pre-formula course board) and it has a distinct advantage with a 7.3. However 7.3 turned out to be too small for marginal conditions (I tried!) and I am adding back an 8.0: I was indeed wandering if the advantage ML vs Is-111 was going to be reduced by a larger sail. (I'll keep the ML anyway, it is a pleasure to sail in tiny winds).
I am sure the 86 slim will cover the CA 52 territory, and if it can take some of the place of the CA 58 I should be set. The standard Is 86 should give a safer overlap with the Is-111, but I am a bit afraid it would be a bit less easy than the slim in the summer 5.5-6.0 conditions so frequent in the Bay Area ... Wondering how much difference 5L make ...?