Public market stocks.
I know this isn't exactly what you're asking but I mention because it's worth considering in your personal decisioning framework (and is my honest answer)
For example, the 30 year TIPS return at the moment is ~1% - I would consider that a truly "safe, real interest rate" return. By that standard, taking out 4% in real dollars has a significant chance of depleting your principal over time.
1% is way off.