Realized that playing with leverage is really a mental game as much as it is mathematical, and I wasn't mentally up to carrying a whole lot of debt, so nowadays, I just do what lets me sleep best at night.

There is no exact mathematical formula for this..unfortunately. 

Mathematics is a very logical subject... with theorems and postulates and structures that follow certain rules...

@George Gammon I agree that using average returns appears deceptive, but it is mostly because people lack basic mathematical understanding.

@Dustan MarshallI still believe that completely debt free must be a very personal journey because mathematically leverage will always have the upper hand.

His teachings are religous based not mathematical. 

Those are mathematical truths that no one will refute (except for flat earthers).

And when you meet four different flavors and they all say the same thing it is so close to impossible to avoid that that it is probably mathematically indistinguishable. 

@Chris Hill mathematically it would be faster to pay off 10k per month than save up 120k/year and throw it at the loan at the end of the year.

Others don't like the idea of owing more money in interest and are against it. mathematically speaking, 40YFRM is an excellent loan for the cash-flow market.