top riders are not using carbon fins, yes G10 does not last as long as carbon it breaks down but i bet you wont be ridding them to end of life anyway.
NOt sure what sold you on 44's but thats pretty big for your size. I'd recommend something 40 to 43. with fins in this size range you need to get a 70cm board. these fins will be too big for a board any smaller. 65cm board get 37 to 40cm fins. I don't know why anybody will get a 65 these days but just in case you find a good deal on one.

Right, with the standard widest allowed boards now, 42-43cm are typically used by many competitors

Peter