Don't look at volatility as a measure of risk, if you need a simple measure of risk, look at market earnings yield vs treasury yield
Here's a shortcut website for the sp500:
http://www.multpl.com/s-p-500-earnings-yieldHere's treasury yield:
http://www.treasury.gov/resource-center/data-chart-center/interest-rates/Pages/TextView.aspx?data=yieldThe first is backed by the earning power and underlying assets of the top 500 companies as selected by S&P (excludes some great foreign companies as well as some of the bigger US companies as well, like Tesla or Netflix)
The second is backed by the taxing power/authority of the US government
If the first is ever approaching the second, your opportunity cost adjusting for risk is better by holding the second, because taxing power of the US government is stronger and further reaching than the aggregate earning power of the sp500 - please also take taxes into consideration, don't blindly sell taxable holdings without calculating what it will cost you in capital gains tax first