Interesting thing about averages, every day has several hours without wind, dusk and dawn are common times without wind. To get a 9mph average the actual wind speed when the wind blows will be couple MPH faster, just about doubles the power! Time to recalculate.

Wind turbine can be designed to handle both conditions, might not be for a first timer. Variable pitch can do it. Suggest to build the larger for the lower speeds, then work on a variable pitch design.
Breezy 5.5 might do it also, plans are available. Another solution is to build two wind turbines, low speed and high. Couple years ago some fella wanted to produce power in 150mph average winds. Antarctica. He did it. Worked much better than solar!!