Which would perform better? 100% stocks or mixture of stocks and bonds?

Its the quality of the securities that you hold that determine the long-term performance.

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Asset allocation is just a risk-adjusted measure

50:50

I would say it depends on what you are comfortable with and what is your circle of competence! Generally, if you understand what you are buying into, it will give you a better ease of mind during corrections and you won't sell out of panic.

No evidence that a portfolio mixed with stocks and bonds have outperform a pure equity portfolio for long term investors.

Useful if volatility makes u sell out and you do not have right volatility tolerance. Or if u trading in abs out of both markets and u are able to time them well