Sorry, I didn't mean to imply that "useful and readable" implies an n <= 7. Small n makes otherwise unintuitive or hard to remember things easier, but there are obviously longer "useful and readable" domains. Note, however, that while overcomingbias.com is useful, most domains in its immediate neighborhood are not. qvercomingbias.com, wvercomingbias.com, etc.
It's important to have a good name but not crucial and it doesn't have to be short.