@Brett Palmer in the interest of simplicity since it seems that is where you are leaning, use the 200k and purchase another rental house outright. Then if the market did tank you are covered-ish. It sounds like your duplex has a good cushion, and you primary could be covered by your w2 if worst came to worst. Then you can make 1500+ a month for your new rental. Take that money and pay down your primary or the duplex. Likely in less than 7 years you could have two payed off rentals. If you are handling two tenants, 3-4 wouldn’t be that much change or hassle for you.
The real estate tycoon wannabes will roll about opportunity cost but everyone doesn’t want to manage an insane number of houses. With two paid off rentals I presume you could double your teacher retirement.
You could also keep 20k or so back as a safety net for vacancy, cap ex, etc. and feel like you are in a very good position financially.
My two pennies worth, sincerely someone that would love to have this problem!