Actually I think the Imperial system is better in this case. I find it easier to remember a number which is an integer in the 20-40 range than a real between 5

Actually I think the Imperial system is better in this case. I find it easier to remember a number which is an integer in the 20-40 range than a real between 5 and 10. I find that in my mind, most of the relevant numbers tend to get rounded up to "a bit less than ten" anyway.