I must say that I don't agree with the Futura 133/10.6 combination. A 77 cm wide board won't work with such a big sail. I once had a Carve 145 (same width as the futura 133) and my 9.4 was fast and early planing with it. I tried it with a 10.3 sail and planing was worse, control bad and speed lower. I'd go for a 9.5 as max. The F133/9.5 wil plane noticeably earlier than with a 7.5 sail.
If you want true early planing the iSonic would love a 10.6 sail and get going really early.
Anyway, in true 7.5 conditions the smaller board will be a lot more fun and it will even carry a 6.5 sail when it gets windy.