Interesting that all this expressed in wind speed, rather than force, which is what causes damage. As a good rule of thumb, 50 mph generates c10 lbs/sq ft, 60 mph c15 and 70 mph c20, so you can see that a 70 mph gust is likely to be twice as destructive as a 50 mph gust, other things, like air density, being equal. It also means that a 70 mph gust of dense, cool moisture-laden air will be a lot more destructive than the same gust of dry, warm air. Sustained Atlantic winds of 70 mph in January are likely to be destructive in the wrong place!