Option 1: Do I take all of my excess cash flow (which I don't need) and pay down the debt as fast as possible - with the intention of refinancing, using the proceeds to purchase other income properties.Option 2: Save all of my cash flow to combine with my other savings to fund another down payment and just do this as quickly as possible (while still keeping a reserve for disaster etc..) 

Cash flow in excess of $200 per door and on track for a return in the neighborhood of ~10%.  

If you already have an ample reserve fund in place for the unexpected emergencies, then using all your excess cash flow to pay down the loan principle should be OK.  

That does seem excessive. 

My MSA has a population in excess of one million and there are no NARPM credentialed individuals within 50 miles.  

Also if subsidy exceeds all closing costs and prepaid excess goes first to buying down the interest rate, and if more is left after that after max buy down it goes to the lender ad profit.

Capital contributions from your lending activity in excess of acquisition costs (if any) become working capital.

A slip and fall of child or hi earning person where the insurance does not over the cost of the injury or possibly a death, they could come after you personally. a car or plane crashing into the property that would be in excess of the insurance that you purchase.

The opportunity cost for stuffing cash in that property are in excess of 20% annually if you invest your cash in decent projects.  

. , not all plans allow excess after-tax contributions.