I did a little FIREcalc meta-analysis to get a better feel for Safe Withdrawal Rates....
I agree, great work! But I'm curious why you used FIREcalc instead of cFIREsim, given the known flaw in [EDIT]
cFIREsim's FIREcalc's bond data
? However, I just ran a few comparison simulations to spot check the differences in the outputs between the two alternatives, and, with the default allocation of only 25% bonds, the discrepancy in the bond return calculation method does not appear to have a material impact on the outputs for purposes of your analysis.
In addition, I have a quibble with this portion of your analysis:
3. The biggest increases in SWR come from shortening your time period. This suggests to me that annuities like social security are hugely valuable, probably worth significantly depleting your nest egg. For example, if you can buy a social security supplemental annuity at age 52 to cover all of your expenses after age 62, and by so doing lower your expected period of retirement drawdown from 30 years to 10 years, you can effectively increase your withdrawal rate on the remaining nest egg from 4% to 8.5% (from green's 95% to blue's 95% line) without negatively impacting your success probability. That means it would be worth spending over half of your nest egg to get that annuity. Short planned drawdown periods seem to make retirement super easy.
This analysis assigns no value to having a positive terminal portfolio value at the end of the retirement period (which may be a valid assumption for some people, but, all else being equal, I think most people would prefer to have something instead of nothing at retirement end (i.e., death) in order to pass on to their heirs, give to charity, throw themselves a Great Gatsby level party of a funeral, or whatever).
In your example, spending half of your portfolio to purchase the supplemental annuity (which would have no impact on your success probability and almost no impact on your withdrawals in absolute dollars) would cost you a historically median amount of $258K in terminal portfolio value for every $100K of your portfolio that was spent on the annuity. That is, if your portfolio was $1 million at age 52, and you spent half of it ($500k) on an annuity, then, at the projected end of the retirement period (age 82, in your example), you would be left with a portfolio of $0 (but, of course, you would still have the entitlement to continue collecting the annuity payments if you continue to live beyond that point), whereas, had you not purchased the annuity, you would at that point have had a terminal portfolio having a historical median amount of $1,290,000. Given that all else is practically equal between the two scenarios, I'd rather have a $1,290,000 portfolio when I turn 82 than have zero dollars and the right to collect $40K per year for the remainder of my life.