I am just using an example with 6% but I felt the the cap gains wash out with the deduction for interest. I just wanted to keep the example simple. I am certain we can complicate this with risk analyis, risk arbitrage and a lot of other variables.

Yes I understand that paying down the mortgage is risk free vs investing in the market carries risk premium. But if we are talking baout 10 years plus the risk seems to go down pretty dramatically.