The biggest argument I have seen is from Mercury Outboard Motors.
They ran several models of their outboards both on E-0 and on E-15, yes, 15, you can argue all you want about the fact it was 15 and the corner station is only 10 but.. Well, you will just be passing gas in my book because the only effect of the higher alcohol content will be to accelerate the damage.
Of the engines they tested, at the end of the test (which was actually fairly short) they tore down all of them
One engine failed before the test ended,, it was burning E-15
All the E-15 engines had serious wear damage
All the E-0 Engins showed only very slight wear issues.
The conclusion was that the E-15 Seriously damaged the engines.
Now, I will not say one should NEVER put alcohol in your gasoline tank,, I mean, I'm from Michigan and did it myself before they started doing it at the refineray.. IN THE WINTER,, but I only put like 1 pint in 20 gallons (That's less than E-2) in fact, Standard Oil's old advertisement "My Advice Sir, Get De-Icer" was, HEET brand Gas Line Additive, just about 1 part per Hunderd if I recall (might be 2) That's E-1 or E-2)
Keep it in the single digits please. LOW single digits.