Yes, I agree that if you want to plane the earliest, a Formula is king, no question.
However, there are other elements that need to be puit into the equation. Do you intend to keep the Bic Techno 148 or do you want to replace that board with either a Formula, UltraSonic or iSonic 127 with a 8.0 + 10.0 m2 sails quiver ?
1) If you want to keep the Bic Techno 148 with your 8.0 sail, a Formula will plane earlier, point higher upwind and downwind than an UltraSonic with a 10.0 sail. However, the UltraSonic would be easier under your feets in choppy water, when jibing or when back and forth reaching. If you cannot waterstart your 10.0 sail yet, both will be a more stable platform (more width with more volume overall than an iSonic 127) when you'll uphaul your sail out of water. The learning curve will be easier and faster with an UltraSonic than that with a Formula for a skilled intermediate, no question.
2) If you want to replace your Bic Techno 148, better take an iSonic 127 for your light weight because a Formula or an UltraSonic would be way too large and bulky with your 8.0 sail in solid winds. Even the iSonic 127 would be the limit with an 8.0 sail (an iSonic 117 wide would be perfect with 8.0 + 10.0 for a 65 kg skilled expert) but given your intermediate skills and the fact that your area is not too choppy when it really blows, I surmise that you'll use 80% of your time the 10.0 sail in 7-12 knots wind range whereas you'll use the 8.0 sail 20% of your time in 12-18 knots wind range, so the iSonic 127 would match that usage perfectly.
In comparison to your current Techno 148 (75 cm width), the iSonic 127 would clearly feel underfoot like a 1 size larger board, the UltraSonic would feel like a 2 sizes larger board and the Formula would feel like a 3 sizes larger board (especially at the tail).
Last edited by Jean-Marc; 23rd December 2011 at 02:38 PM.