I'm fortunate enough to have about 100K saved up but haven't really done anything with it besides putting it in money market accounts and some into stock index funds. 

with that size of mortgage, I would be trying to move, and then invest in RE.Otherwise, just put your money in an INDEX Fund

Especially in this far too over inflated pricing index.

Just look at the Case-Shiller historical index. 

The apartment complex I watch as an index for college housing is down far more than 1.6% right now. 

That was 15 years and 650 deals ago so I don't remember the details, but it's easy to remember the two checks to the IRS and in both cases the payment was a reasonable expense and the deals were profitable at the end of the day.As to your second question, "IRS" and "Federal Tax" are two common ways that different counties index the same document.

It depends where you live, the affordability index, buy vs. rent comparison etc.

Obviously, the market is doing great, and I am going to expand into rental RE, but I have to say, all three of my "Index Funds" have been doing awesome over the last two years.  

The Shillers PE and the Stress Index.http://www.multpl.com/shiller-pe/tableThe shiller PE is definitely high right now but the stress index is negative.

Some counties will also have a 'well index' where you can check all of the surrounding wells to see how deep they are, gpm, etc.