My thought is that... if you build a machine that does nicely in low winds, you'll probably have more power than you know what to do with in the high winds!
I would think that most machines that start easily, and have a good low cutin speed and work very well in low winds, will also do fine in high winds.
there are however many machines that do fine in high winds, but very poorly in low winds.
I think the key to getting power in low winds is having a machine that turns freely, and sweeps a large area (big prop). Power available from the wind is related to the cube of the windspeed. So.. there's 8 X the power in a 10mph wind that there is in a 5mph wind. There's 64 times the power in a 20 mph wind that there is in a 5 mph wind. So, basicly there's not much power available from a 5mph wind... but if you get a little bit at 5 or 6 you'd be doing very well, and if its producing @ 7mph it's probably making a gob of power at 20. There is practically no power available below 7 mph unless the machine is huge.
Easier than building 2 or more machines trying to optimize each one to a different condition might be putting all that effort into one machine that works nicely across the board.
You've asked some interesting questions... and it sounds like your planning to build something. I'd highly suggest you get a copy of "Windpower Workshop" - super book, fun reading... and it will answer all these questions and many more. You can get that off our shopping cart, and I believe Ed stocks it at www.windstuffnow.com.
