if we go by a 25% equity allocation using the traditional benchmark worst case time frames that allocation would have failed 20% of all the time frames at 4% and 69% of the time at 5%
we also know that using longer term more volatile corporate bonds in the mix in the trinity study resulted in more failures than bill bengans 5 year bonds . so not sure how really long term bonds would have done . you would possibly be locked in to lower rates for a very long time in a rising rate environment .
with gold tracking the cpi and not much more we can't say what effect gold would have on the results . my feeling is buying the gold at the expense of buying equity's would not have resulted in better performance since equity's far and away had much higher returns over most of history .
we can't predict the future of course but my guess is the pp would likely have measured more like a 25% equity portfolio being limited to about 3% as an swr not 4% over those benchmark time frames and certainly not 5% under the same benchmarks .
I thought you already agreed that it's pointless to talk about how the PP would have done during the time periods you're talking about here.
What we do know is that since gold has been available as a freely traded investment, the long term return of the PP has been fairly close to that of even a 100% stock portfolio (within the margin of error, depending on your start and end dates) and that its volatility and max drawdowns have been significantly less.
How can this be if (as you keep insisting) the amount of stocks in your portfolio is the primary driver of long term returns?
What you seem to be missing is that gold does not simply match CPI, but is a volatile investment (as volatile or even more volatile than stocks). And that long term bonds are also volatile. And that mixing these three highly volatile assets together creates a very stable portfolio. BTW - you're never "locked in to lower rates for a very long time in a rising rate environment". You sell long term bonds after holding them for 10 years and rebalance as well, so in a rising rate environment you'd be rebalancing into long term bonds meaning you're benefiting from rising rates as they rise.
The theory that the assets act together to shield you from the wild swings in value that a mostly stock portfolio endures has not been invalidated in the past 40+ years. In 2008 (on an annual basis) a 60/40 stock/bond portfolio dropped about 25% while a vanilla PP (using t-bills as cash) dropped less than 2%. Rather than require a 33% increase to get back to even the PP only needed a 2.04% increase. Note that this particular case was covered by Browne's theoretical framework (long term bonds will strongly react in a deflationary environment) but he had never seen an example. This is at least as out of sample as the years you seem to be focused on in which the PP could not have existed.
if i was going to use the pp in retirement and i really wanted to have the same conservative level of a swr that a 4% swr gives a conventional allocation of 60/40 or 50/50 i would start the pp based on a 3% draw rate .
if after the first 3 years in retirement the portfolio was 2x what i started with i would take another 10% raise on top of inflation adjusting , 3 years later if i was still at a level of 2x what i started with i would take another 10% raise.
better to start with lower expectations and go up then plan a life around a budget that may have to be cut .
If after 3 years the portfolio was 2x what you started with? To double in 3 years requires a return of 26% per year. That clearly isn't going to happen with any portfolio, so what do you really mean?