Mostly because:

1. 40% because I think Berkshire Hathaway is almost certain to outperform the S&P 500 (VOO) or broader indexes over 10+ years. But VOO or the indices you suggest are reasonable alternatives;

2. 40% shorter term US Treasuries because inflation cycles take many decades to run, and the period of low rates and low inflation is over. Long term bonds lose a lot of money during inflation and the accompanying rising rates. So maybe 15% BIL, 15% VTIP, 10% VTIG.

While rates can bounce along the bottom for many years, trend in the coming decades is higher inflation and higher interest rates. And if the market crashes, and it most certainly will sooner or later a time or two over the next couple of decades. short term US bonds are as safe as it gets.

The last complete interest rate cycle took 75 years. Rates bottomed in 1946, peaked in 1981, bottomed in 2021.

3. You can do an index for this last 20% or fold it into the above holdings. I plan to recommend to my family to hold it into my highest conviction longer term growth stocks at the time. This is risky because things change and I won't be around to advise. I'd probably risk 30% of this 20% in Bitcoin ETFs.

You can't pick and choose piecemeal here. This is likely safe as a package.

I make no recommendations to anyone, could change my mind about this at any time, and I'm wrong a lot.

GL