Question - Keep
thinking about cashing out the stocks and using the money to pay off the mortgage.
In finance, you address this as a "present value" calculation. If you have a fixed mortgage, you only have uncertainty on one side of the equation, the stock market side, but if you have a variable mortgage, then you have uncertainty on both sides, which adds to the complexity.
The simple way to look at this is to compare the rate on your mortgage vs your expected risk adjusted market return and keep your money in which ever is greater.