I had the Xantos II and the Powerglide that were all very similar in design/size and found for me at 100Kg a 7.8 V8 was the max size with a 44 fin and at that point it was really trying to chick me off even with the straps on the edge, I bought a better fin with a narrower chord in the same size and it was better but the narrow width was hard work compared to the Carve 145 that I replaced my Powerglide with a couple of years later that was at least 10cm wider and could carry a 9.0m just!
I do have a very worn out Sputnik 290 120ltrs that I sail with a 42cm fin and the 8.0 which is ok! It's a bit tricky in the gybe but otherwise it sails ok, which is why I thought the 295 would carry more,being quite a lot wider in the tail with more volume.
If you'd been around a while you'd understand...
Starboard hatred