When should I pay off my mortgages?

[Steve S.]

One of my goals has been early retirement. 2 of the rentals I own are going to help achieve that goal. Here's a quick summary of each:

1) 30 year mortgage, 4.125%, $1,350 / month rent, 30% equity

2) 30 year mortgage, 3.75%, $1,595 / month rent, 45% equity

I've owned both of them for < 4 years. I could pay off both in the next 2 years and own them free and clear.

What I'm trying to determine is how quickly should I pay off rentals. My goal is to cash flow gross $10,000 per month from my rentals. That coupled with other investments, 4% rule, etc will allow me to retire young at a level I'm comfortable with and allow me the time to focus on creating value through ventures other than selling my soul to corporate america.

Obviously, these 2 prroperties aren't going to gross me $10,000 per months, but if these 2 were paid off and i had 4 more like it (paid off), i'd be grossing about $10,000.

Thoughts on how best to decide when to pay down more quickly, especially with the markets generally being at new highs these days?