I sailed my iSonic 122 with a 6.5 metre no-cam 5 batten freeride sail before I switched to a 7.0 cammed sail. The 6.5 worked surprisingly well. Speed was excellent and planing quite okay. Only drawback was pure bottom end power and max control. In really harsh conditions I would get up on my toes and loose a little control as the centre of effort is situated higher and moves more around on a freeride sail. Anyway jibing is a dream with a no-cam. You won't win a serious race with a no-cam though.
I've tried a weed fin on my iSonic too. No good experience. It works okay on a freeride board but the iSonic lacks lift an pointing when used with a weed fin. The bigger iSonics are quite wide tailed and they need a fin to support this. Pure downwind speed wasn't good either. Interesting as my former S-type 115 was more quick downwind with a weed fin than with a slalom fin. On the other hand a weed fin can be very controlled as it almost never spins out (or catches weed).