E85 is 100-105 (R+M)/2 octane. A couple of points lower than typical unleaded race gas (110), or leaded (116) but still much better than "premium" at 91 or 93 depending on area in the US. Not sure how many people this is news to, but it's at least one person.
My personal experience with E85 has been great. Made a ton of power and was able to run leaner, and more advanced safely. It's not only chemically resistant to detonation, it cools the intake charge much better than gasoline. E85 is so much better than gasoline it's hard to not run it. The only unknown is how long the rubber/steel would last in any given car not specifically designed for it. I'm not trying to stop anyone from using it, I'd just like them to be informed.