I had the chance to sail the 2010 F131 and the isonic 121 at Furteventura last September - No doubt, both boards are fantastic.
Conditions were marginal, 5 - 8 m/s, and I was restricted to a NP RS slalom race sails, size 6,7 m2, wich was the biggest they had at Rene Eglis.
I was a wopping 100 kgs at the time. Both boards had the 42 Drake fin, which was not ideal.
Not surprisingly the isonic release faster thanks to the sharper rails. Jibing is excellent as well - It is actually quite easy to plane through.
The F131 is also super fast with the proper setup, and has the best jibing qualities of any board I have ever sailed.
Both boards planed equally early, though it must be said that I expect that a different fin would have helped the early planning quite a bit, lowering my thereshold from around 7 m/s to at least 6 m/s. The same goes for increased sail size. With the ideal setup pre 6 m/s planning should be achiveable for me, and the makes a great difference in the outer Oslofjord area which is my hometurf in the summertime.
I am super impressed with the shapes - the both deliver the sensation of riding a "small" board, which is paramount for the fun factor.
The Isonic though is a bit more direct an nervous, which makes for more tiering and less relaxed ride. The Futura is the definition of Smoothness and control. Still it made me feel almost as fast as on the Isonic - and I was still outspeeding all other sailers by a good margin.
I was lucky to have access to the woodcarbon edition - And I would favour this for the F131 - especially if early planning and top bottom end is the focus. For smaller boards wood is probably still going to be my choice.
Hope this helps - best of luck.