From the Windwing site some info on wind ranges.
Everyone's been asking and it's tough to say because they're so "rangey". But here's what they came up with....
"Windwing has been very reluctant to publish wind-range charts or give wind minimums or maximums for the kites we make because we feel that there are too many variables (rider weight, board size, water conditions, rider ability and style, air and water density) for this information to make any scientific sense, in addition to the fact that most people do not have access to accurate windspeed information anyway (Do NOT believe what the wind-pager is telling you -- those machines are often way out of calibration, and hand-held wind meters do not tell you what is happening out on the water -- could be much stronger or weaker than where you are standing).
At Windwing we believe that you should never rely on any such chart or printed material for selecting your kite size for any given conditions.
With the above disclaimer in mind, here is what Flash, JB, and Bob came up with from their first-hand experience with these kites, for an average sized rider with a "normal" board: "