Yes they are tested (or supposed to be) to well over 100mph. (Proven, were designed in and for the west coast of Scotland) The idea is that the blades cone themselves, reducing the surface area presented to the wind. I have stood underneath the turbine (mine is on a 15m mast) in 70mph winds and it does 'cone' but not as much as I expected. Of course this is the advantage of the Proven design, in that it still produces max power in very strong winds, where other models (and commercial) have to turn out of the wind... to protect themselves. - not sure whether they still produce any power in such cirumstances.

Peter