> assuming we do an extra payment toward the principal every once & a while

At the risk of veering into financial advice, paying extra principle early is almost never a good idea. Instead, put that money aside into an investment account and use it to pay off the mortgage once the sum is greater than the balance.

Assuming markets beat your interest rate, you'll have a higher return and you have the emergency fund in case something catastrophic happens. If you pay that to the bank you can't get it back in an emergency, and you will only cut down on the front-loaded interest--which will likely be under market returns.