I ran E85 for many years on my turbo Volvo wagon, which was running about 20 - 24 psi of boost. Very ping resistant, to the point where it was possible to advance tuning pst peak and start hurting power, still without detonation.

I first started doing it way back when, 2007-ish time frame, using a standalone Megasquirt injection computer. It didn't have flex fuel capability, but I (mis)used the nitrous functionality - added an external switch to flip between my dedicated gasoline and E85 spark/fuel/boost tables. Advance the timing some, 25 - 30% more fuel, higher boost on E85. I'd just run it really low on one fuel, fill up with the other, run it a few seconds and flip the switch. And the E85 tune was always elusive, I was doing a lot of ongoing tuning.

Eventually I put an MS3X ecu on it, which supported flex fuel, and added a GM ethanol sensor on the return line. Where I discovered why the E85 tune was always a work in progress - the % of ethanol in a given E85 pump was pretty variable. Anywhere from 30% up to the advertised 85%. The flex fuel setup worked a lot better, interpolating between the two sets of tables based on the %, with a configurable curve.

Basically a little ethanol in the gas goes a long way, it's not a smooth curve between E10 and 85% E85, at least in terms of the effective octane rating. The good E85 acts like 110 octane fuel more or less, it's like race gas (other than the 'lo calorie' aspect).

I've since put a turbo 5.3 LS V8 in it, running lower boost (7-8 psi), and I'm running pump premium in it for now.