Experience from using React for many years tells me. Rarely have I needed to optimize anything related to react to make something visibly snappier, and most of the time it's not really React's fault.
And there are some benchmarks that show SolidJS and some other things are faster than React at specifically what React is doing (like dom manipulation/reconciliation etc).
How can you know this? The only scientific way to approach this question is with real-user metrics and analytics.