Back to the original question: No, E10 won't hurt your engine.
When ethanol is blended at the blender to get E5.7 (CA average) or E10, or whatever, the hydrocarbon mix is altered, including the additive packages. 87 E10 is still 87 octane. It doesn't run hotter. 100% ethanol is around 105 octane, and helps the blender "stretch" the octane components of the fuel. In California, only one supplier has ethanol free gasoline, and it is not adverised.
For those of you old enough to remember the fuss over the switch from leaded to unleaded, a similar brouhaha is going on with the inclusion of ethanol in gasoline. It is a new, to many people, fuel, and lots of odd things are being attributed to the ethanol- e.g. flying cows, off the line acceleration, pink elephants, massive HP gains, decreased fuel economy, altered emissions, kangaroos in upstate NY(to my knowledge, only the latter two or three are true).
This is a plea for common sense. Look at reviews at national organizations, like Consumer Reports. Don't believe all that you read in the media, especially the internet.
Do believe that a great number of petroleum chemists spent a lot of time and money getting gasoline ethanol blends that work. Why? Because a lot of money was riding on it.
If the fuel can be demonstrated to be bad, the oil company that created the blend is liable for the damage. Given the number of cars on the road, that is not something that they would want to have happen. I'm not saying that one brand of gasoline may or may not be better, but I am saying that if someone is disparaging the fuel, they better have real, statistical data with large numbers of engines. "Ah had a buddy whoz gran pappy had this ol engine that jus plain melted..." Don't believe me- go read data at ASME, CR, EPA, CARB, etc.
Bottom line:
- worry about the brand,
- worry about how fresh the fuel is, and
- worry whether or not the stations' fuel tanks were just filled (which is bad because it stirs up debris- give it a day to settle again).
- Don't worry about whether it has ethanol in it.
Why using brand X, my first car went 287,000 miles...Oh, wait that's anecdotal...
Happy tractoring folks...
All the best,
Peter