This is what I've tested with my 65 kg:
Lower wind range:
1) Formula + soft 70 cm fin + Code Red 11.0 m2 sail : start and sustain planing as of 6 knots.
2) Ultrasonic + 62 cm fin + Code Red/Refelx II 11.0 m2 sail : start and sustain planing as of 7 knots.
3) iSonic 127 + 55 cm fin + Refelx II 11.0 m2 sail : start and sustain planing as of 7 knots.
Upper wind range:
1) + 2) + 3) remain in full control up to 12 knots steady wind. With a narrower board (HS105) + 55 cm fin, it's still under control up to 15 knots peak gusts for my light weight.
The lower wind range between a North S-Type 9.5 and a Severne Code Red/Reflex11.0 m2 sail is quite significant but irrespective of the board + fin size combo : 2 knots later with a 9.5 m2 sail; 3 knots later with an 8.5 m2 sail as compared to that with an 11.0 m2 sail.
The Serenity is quite special as it doesn't plane as a true planing board, i.e., cannot climb over her own bow wave and accelerate further and further (topping speed is about 13.5 knots board speed, not higher). Wind range with an 11.0 sail and the stock stiff Drake 70 cm fin : 2-8 knots wind; board speed is twice that of wind speed. Check following movie of Serenity + 11 m2 sail on a fresh water lake in 3-5 knots wind (http://www.youtube.com/watch?v=V97ikRFQDdU
) and in 5-7 knots wind (http://www.youtube.com/watch?v=KjfmQcSXGRA
You might think an 11.0 sail is too big for a 65 kg, but once sailing, it's no big differenece with say an 9.5 or a 10.5 m2 sail in the hands. As for my home spot where I usually have 2-7 knots almost 3 days a week and 7-12 knots almost 2 days a week between March and November, the addition of an 11.0 sail to my sail quiver has increased the number of planing session by a factor of 2. The addition of the Serenity has increased the number of gliding session by another factor of 2. With that quiver, I can go windsurfing when I have a free time slot, and not when there is wind. That's a huge improvement in quality TOW and efficient time management outside the office: no more wasted time sitting on the beach and waiting for a minimum wind limit to materialize. Sure, the Serenity, 550 cm mast, rolled 11.0 sail and long boom are large items to lugg and carry around, but it has been worth the trouble since 5 years: no pain, no gain.