I'm not a team member, but I do have some experience as I had a Carve 145 (very much the same as your C151) and now I have an iSonic 122 (a little narrower in the middle but wider in the tail but less volume).
My experience is that the iSonic is a more technical board to get going. It's short and has noticeable less volume. Acceleration is very impressive compared to the carve and top end control is way superior - you can really max it without loosing control even with quite small sails. The ride and stance is perfect.... The iSonic jibes brilliantly in harsh conditions compared to the Carve (which is quite good).
Average speed is higher on the iSonic but actually I have measuerd a higher top speed on my carve (one knots difference in favour to the carve but I will beat it with the iSonic;-).
I (95 kgs) use a 46 fin as max with a 8.5 sail, and the iSonic can be sailed with quite small fins. Pointing is better on the iSonic.
Early planing? This one is difficult as it really is a matter of your personal style. The volume and length of the carve will for sure be an advantage if you are a more "lazy" sailor waiting for the gust to do the work. On the iSonic, with a more active technique (foor stance and pumping) you will get going as early as the carve - especially at 64 kgs. For my weight the iSonic is quite submerged at the beginning.
Today I see absolutely no reason to choose a carve (or futura but I dont know these) to the iSonic. My iSonic is for sure the best board I've ever had (and I've had a lot)