Thank you for the nice charts, AdrainC. They make it easy to slide to see any sub-period, such as 2020 or 2025. We can also see at a glance the wide range of one-year returns versus the narrow range of 27 year returns. I have a chart (that needs updating) which shows the returns versus the number of trailing years. It looks like a trumpet, with a typical range of 30+ percentage points for one trailing year and about 4 percentage points for 25 or more trailing years. Never be too impressed with 1, 3, 5 or 10 year trailing returns.

Back to the question of asset allocation: Buffett recommended 90% S&P 500 index and 10% short term Treasuries, while Bogle recommended a bond percentage equal to one's age (76% for me). Quite a difference. A Kelly analysis which I posted here before (Sorry, I have to look up the reference.) recommended an allocation based on the percentage points by which one expects stocks to outperform T-Bills. It came down to:

expected stock return minus T-Bill return (percentage points), allocation to stocks

4 percentage points, 100% stocks/0% T-Bills
3 percentage points, 75% stocks
2 percentage points, 50% stocks
1 percentage point, 25% stocks
0 percentage points, 0% stocks/100% T-Bills

I expect the S&P 500 to return about its earnings yield over the next 5-10 years, or 3.5%, and T-Bills to return about their current yield, 3.5%, so if I followed this analysis I would have 0% allocation to stocks and 100% allocation to T-Bills.

Therefore the best allocation for me is somewhere in the range of 0% in stocks (Kelly analysis) or 90% in stocks (Buffett recommendation). Well that sure narrows it down :)