I think it's hard to see now with so many different types of market caps nowadays. Also your statement above seems to be without considering the psychological side of a person as well as the actual current market situation, so I think this is just a word of motivation and not a definite theory to rush into practice.
I am afraid what you are write above will be read by newbies who are inexperienced and that will make them fall into serious losses.
If you are doing that by hand, I would suggest just the top 100 would be more than enough, probably even too much. In that scenario you could find which one of those top 100 have the lowest difference between the lowest and the highest in the last 30 days and see the lowest volatility.