SORR risk is only a risk if you retire on a shoestring, with barely enough money.

A fact too often emphasized. It can seem hard-hearted to tell someone "there is no arithmetical solution to your problem, you just don't have enough savings". But it's better to know the truth.

Broadly speaking, there are three populations of retirees.

(1) Those that don't have enough money to support themselves till death. No amount of fiddling with formulas will help that situation, they must rely on whatever pensions are offered them by governments or perhaps an ex-employers or kind hearted relatives.

(2) Those that have considerably more than enough to support themselves. Again, fiddling doesn't matter much, they can just buy SPY and live comfortably from the dividends, as Mr Buffett has suggested for his widow.

(3) Only in the middle ground does doing the optimal thing even become worth talking about because longevity risk rears its ugly head: trying to steer a narrow path (which may or may not exist and generally can't be seen in advance) between outliving your savings pot versus never getting any benefit from the bulk of your savings. 90% of that optimization argument goes away for those who stand back, look at the numbers, and realize that only pooled schemes make sense for the best solution to longevity risk. Axiomatically only a small fraction of people will live to unusually ripe old ages, so a pooled pot for those people can be funded cheaply with plenty of assets for the few that end up needing it. It's almost perverse to expect each and every person to squirrel away a huge fraction of their hard-earned assets against an eventuality that definitely won't happen for most of them.

Consequently I generally suggest to people in that middle tier a two pronged approach: buy longevity insurance (usually meaning a horribly overpriced annuity) to cut off the "longevity risk" past a certain age, say a pinch past your statistical life expectancy. That usually takes a minority of your funds, maybe 10-20% depending. Then spend the rest of your savings in a more or less straight line until that age, which is a hugely simpler problem. The solutions to that spending problem that could be explained to any spouse or mother-in-law. The goal is to divide the pot in the ratio that gives you around the same real income both before and after the switch to using the annuity.

Alas there aren't many good longevity risk products. I believe the best is a "mutual inheritance fund", cousin of the tontine. A person retiring at 60-65 might reasonably expect to cut off ALL their longevity risk with a one time contribution equal to 1-2 years of target future real income. Alas, MIFs aren't available. The closest to that available in the US seems to be the TIAA "traditional annuity", which varies its payout upwards beyond a modest guaranteed baseline based on the investment returns and mortality stats of its members. The only other broadly available choice is an annuity from an insurance company. It's generally best to buy that at the last minute, not in advance as a very-deferred annuity, for a variety of reasons.

Jim