I have put a lot of effort into an Excel spreadsheet. If you want I am willing to email the sheet to you to help you out with future decisions. Onward!
Google terms that "are in parentheses" if you don't understand them.
Today's lesson in Finance 333 covers the concept of "Spread".
"Spread" is the concept where you try to earn a Return On Investment (ROI) that is higher than your Weighted Average Cost of Capital (WACC). You take your yearly "net income", divide it by your original purchase price, and you get ROI. This ROI should be higher than your WACC (this would just be your cost of borrowing if you own the property by yourself).
All of my comments below assume you earn 10% ROI in your area.
The value of this option depends on two things: the market rate of return in your area and the rate of T-bills. If your ARM stays at 4.875% then obviously it makes sense for you to keep your cash on hand and re-invest that money into a new property.
Also: you only have to pay PMI until your LTV gets below some certain percentage. I think you can quit paying PMI when your LTV hits 80% (check your promissory note).
If this building originally qualified as FHA, then why not consider getting an FHA fixed rate mortgage? I got one for my first building and I didn't have to pay points.
In any case, with the loans that you presented here the 15 year fixed loan is absolutely a better option than the 10 year fixed. The rate of return is higher for the 15 year loan and obviously cash flow will be better since you are taking longer to repay.
It's kind of hard to compare your original ARM with the 15 year fixed, but here's what I came up with. At 10% ROI, in order for the 15 year fixed loan to be a better option your ARM would have to average more than 6.1% over then next 16 years. This is likely, but I'm not sure how likely and I'll leave that decision to you.
The choice to pay off a loan mostly depends on your ROI. At 10% ROI it is bad business to pay off the loan, but if your ROI is low (say, 6% or less) thenpaying off the loan makes sense.
For anyone else reading this message here is something you all can use: when you pay off a loan you are getting a guaranteed return of X% (where X% is the interest rate on your loan). This is why it makes sense to pay off your highest rate loans first because they give you higher returns for paying them off early.