The 2010 Futura boards include 133, 141 & 155. Why not the 155?
I sail Formula and need an 11.0 sail to plane in 7-8 knots, plus if I hit a hole, I will come off plane. I weigh 77 kg. Normally, I will not go out unless it's blowing 6-12 knots at a minimum because of the puffy conditions of lake sailing.
Realistically, I don't think you will plane in 8 knots with a 9.0 on either the 133 or 141, and if you do, you will not stay there long. However, the 155 will give you your best shot with a lot of pumping. If you get one additional sail, a 9.0 would be your best bet. If you want to add two larger sails, then I would go with an 8.5 and a 10.0 with the 155.
The iSonic 150 is another option since it's wider tail will help you plane a little bit earlier. Take a look at this previous thread and you will be overloaded with light wind planing information.