I was thinking about this more.

Alpe d'Huez is 11% average, I believe. (They do their roads differently, so the switchbacks are dead flat and the part in between is scary steep, but I digress.) Anyway, when I rode that back in 2003, I remember thinking it was the hardest ride I had ever done, after the 2002 Death Ride.

So 11% is pretty scary steep average.