http://www.taxpolicycenter.org/statistics/household-income-q...
http://www.taxpolicycenter.org/statistics/household-income-q...
From Merriam-Webster: a social class occupying a position above the middle class and having the highest status in a society
Many of the HN regulars are upper income, but very few would qualify as upper class (most of us lack the political and social connections).
Additionally, if the wealth distribution curve for the country is basically a backwards "L" with the bend at the ~99th percentile, the difference between the 60th and 80th percentiles isn't really meaningful since the "upper class" is clearly the 99th percentile.
Edit: obviously there are also social caste connotations that used to be applied here too, but I'm only interested in the economic definition.
1: http://www.nytimes.com/2003/01/12/opinion/the-triumph-of-hop...