The Futuras are super nice freeriders, but if you're used to full on slalom boards, I think you will find iSonics more fun. The isonics are so easy in jibes and stuff, that there is not much to gain with a Futura once you're "slalom ready". The big thing with the Futuras in my opinion is that they offer almost the same performance as the iSonics (regarding planing, speed, upwind, control etc etc) with much less technique input from the sailor. But when you have the technique you can get more performance right across the board on an iSonic.
I think you should try out an iS86 if you have the chance. It's still a fair bit wider, especially in the tail, than the CA52. I think you will find it quite well positioned in between the iS111 and CA52. It's an awesome boards also for a light weight, non slalom racer like myself. Even though its lower volume than the CA58, I think you will still find it big enough. And the iS86 stems from a magic line of boards from way back. Anybody will tell you this size has always been a real gem of the range. No doubt, this is something you feel when you step on the iS86. It's one of those rare boards that just "have it".