I would probably be happy if I was confident I wouldn't need the cash for 5 years. If everything tanks in the first 3 years or so you know you'll have to tighten your belt a little bit to make up the shortfall. If it tanks in the last year or two before you need it at least you've had a few years of growth and you can always gradually pull some out over the last year to limit possible losses. (Just like you should with a pension.)
If you might need the money within 5 years then I probably wouldn't bother
Well, you'd have to count the dots! Or I could dig out the script and data later on. But it's something like 80-90% chance of positive return and most of the time if you have a negative return it will be small magnitude
I did exactly that here: https://www.lfgss.com/comments/16283312/
I would probably be happy if I was confident I wouldn't need the cash for 5 years. If everything tanks in the first 3 years or so you know you'll have to tighten your belt a little bit to make up the shortfall. If it tanks in the last year or two before you need it at least you've had a few years of growth and you can always gradually pull some out over the last year to limit possible losses. (Just like you should with a pension.)
If you might need the money within 5 years then I probably wouldn't bother