In an ABC News story on changing hurricane intensities NCAR scientist Greg Holland asserts,

“Remember, for each 10 mph increase of wind speed,” says atmosphere scientist Greg Holland, “there’s about 10 times more damage, and 20 times more financial loss.”

There are those who argue that damage is proportional to the sqaure or even the cube of changes in wind speed, but no one I am aware of who argues that there is a factor of 10 or 20 per 10 mph. This would equate to a difference of 10^8 or 10,000,000 times more damage beween a category 1 and a category 5 (i.e. from 75 mph to 155 mph).

Empircally, when we look at normalized hurricane damage over the past 106 years, we find about 100 times more damage in category 4/5 storms than category 1.