Using Shiller's data, I explored what withdrawal rate would preserve capital over the whole period for which he computed PE10. I think the period in question was something like 1880 to 2009. I found that a withdrawal rate of something like 83%/PE10 would leave the initial sum intact in real terms after 129 years. I believe PE10 is currently about 24, and I usually round the factor of 83% down to 80%, so I would say that you could take 3.3% (less fund management cost) from a 100% equity portfolio, at the moment.
(Note that the withdrawal rate is not fixed, you continually recalculate it along the way. This doesn't make income very volatile, it's not affected by changes in the price of shares, it only varies with the ten year average of profits, which is a relatively stable quantity.)