All my Stihl equipment calls for 89 octane. We have blender pumps here. Which means that the first gallon or two is whatever was pumped last. I assume that was the lowest octane. So to be sure I got at least 89, I get 5 gallons of 91. E0 is rare and expensive here so I use the commonly available E10. Between treating it with stabilizer and rotating fuel every 6 weeks or so, it's fine. I have multiple pieces of 20+ year old equipment that's always had E10 used in it and are still on the original fuel line and never had a carb rebuild or replacement. OTOH I cleaned out a lot of gummed up motorcycle carbs back in the day before ethanol in gas. If you leave fuel in the carb it can gum up the passages wether it has ethanol in it or not.
I used to run half unleaded race gas and half pump gas in my competition off road two stroke motorcycles. I had some detonation/overheating problems on some of them. Also the race gas lasts longer. But it was super expensive then and I'm sure it's more now. It's not worth it for saws and other OPE.