RE: iSonic 105, high winds, lightweight sailor
Regarding smaller weed fins, I'm very impressed with the asymmetrical Duo Weed fins made by Wolfgang Lessacher. I have a smaller than normal 28cm (Duo Weed 100% carbon 28S) that I bought that's simply a wonderful fin. Also, I have recently acquired a Duo Weed 100% carbon 34cm too, and while I've only had a couple sessions on it in combination with my 8.3 sail, I'm similarly stoked with its great performance.
Lessacher's fins are super resistant to spinout or crabbing when pushed hard to windward, and they're nearly as fast as my Tectonic Goldwing slalom fins. Interestingly, they achieve such solid drive without without the forward offset associated with most other brands (Tangent, True Ames and GSport). You might want to consider looking into them. It's my understanding that Roger Jackson has acquired some of them in the past, so it might be possible for you to try one of his (I know that you met up with him in your area very recently to try the Gemini). In the meantime, you can check out more about Lessacher's fin designs at his website below: