https://m.youtube.com/watch?t=909s&v=MtCJS70sEf0
This was pretty good but I would have likes to see some other stuff, mainly when you can no longer run 93 octane practically due to the engine. And no, "everyone knows 13:1 requires race gas" is not evidence.
Their Rocket brand E85 was higher octane than what's at the pump but I think their conclusions are still valid.