"Power factor" is just applying a simplistic equation to something that's not so simple in real life. As 45_auto showed with his Suburban example, your "power factor" doesn't really mean all that much when actually applied to real-life examples.
I don't believe there's many people out there defending their life with a Suburban, however there might be a few.
I do have to disagree that power factor does not mean much in real life examples, I believe it does when we are talking bullets.
Again I go back to the Philippine-American ( Philippine Insurrection) war where the 45's were getting the job done and the 38's were not
Going back to my days of bowling pin shooting, to take a pin off the front of a regulation pin table with authority a 210 power factor or higher was best.
My 45's making a little over 210 power factor would pick the pins up and slam the pins off the table, a 9mm would not even take them off the table.
As I said in my other thread, I really don't care what anyone chooses to use, use what you shoot best and practice with it often.