It's funny, some of the misconceptions people have of fuels. And believe me, they're all a result of our OIL DEPENDENT economy, and the myths they spread. Ethanol doesn't burn much differently than regular petrol. In fact, it DOES burn cleaner. Look at the chemistry and you'll understand. Ethanol based fuels have been used in Brazil, for example, exclusively! Yes, that's right, they're fuel pumps down there are about 90% ethanol, the remaining 10% being diesel and such. And I'm not talking mixes here. It's pure industrial grade ethanol. The reason behind this is that they don't have access to cheap oil like we do, but they have a hell of a lot more corn. Using fermentation processes, they convert that excess corn into ethanol and viola! You have cheap, clean fuel. People have been trying to do that here for years, using corn and other crops, but of course, that has been pushed under the rug. See, we could be oil INdependent.
If you have mixed fuel locally, and it's cheaper, use it. You won't have any problems. Besides, it's in such a low percentage anyway that it makes little difference.
As for octane ratings, they DO NOT have anything to do with the cleanliness of fuel! I HATE when I here people say, "Yup, I put in the better stuff, octane 94! Duh!" Why is it better? Because it costs more????? There's a reason why auto manufacturers rate engines at various octane levels. It all depends on your timing and such. If your rig is built for 87, use it, unless you've played around with timing.