These numbers are relative to a standard where 5.0 is the average for a professional at one's level of experience, 4 is the minimum, and 6 is about the level where people get promoted. If you're consistently 7-9, you're overqualified for what you're doing and should either get a promotion or another job. In this light, I feel comfortable assuming that in normal situations people average no higher than 6.0, although some people vary more than others.

I was high-variance when younger but I learned to become middle-variance over time. It's a necessary aspect of career maturity. So I probably swing between 4 and 8. I can hit 9 but it's not sustainable (although today's 7 was the 9 of two years ago for me) and before I find myself anywhere near 3, I do everything I can to fix the situation (possibly getting another job).