Not on the team, but here are a few points.
At 90 kg, you will not plane in 5 knots on anything with any sail.
Your best bet for the earliest planing board is the iSonic 150, a wider board both at the mid point and the tail than the Futura.
All of the boards are great below 15 knots
Even with the iS 150 and your 8.5, the threshold for planing will be about 9-10 knots at best with a lot of pumping. If you want to get going in 7 or 8 knots, then you need a much larger sail. The 9.5 will be a good choice, but an 11.0 will give you the best bottom end (new mast and boom?).
The smaller iSonics are a more technical ride than the Futuras, but I don't know anything about the differences in the larger boards. Someone from the Team will have to help you here. They can also help you with the WC or Wood choice.
Hope this helps a bit.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.