octane effects power and engine temp?

[j.fro]

This is slightly off topic, but may be of interest. Occasionally I have access to non-ethanol 93 octane fuel. I keep track of my mpg and maintenance using an app on my iphone. I find that with the non-ethanol I get about 1-2 mpg better highway mileage, and that it improves another 1-2 mpg in the warmer months. Here's the skinny:
Summer, non-ethanol, 26-28 mpg
Summer, ethanol, 25-27 mpg
Winter, non-ethanol, 24-26 mpg
Winter ethanol, 23-25 mpg
This data was collected since mid May 2013 over 23,000 miles in a 1999 911 C4. I had noticed similar trends earlier in my 2000 986S.