litesong's Profile | Fuelly
Picked 3 consecutive tank in Dec 2014 (5, 10 & 15% city driving) using ethanol over 891 miles you used 24.98 gallons for and average a 35.7 mpg.
Closest month I could find 3 consecutives using non-ethanol was Jan 2014 with similar (10, 10 & 15% city), over 1089 miles you used 29.4 gallons for 37 mpg.
1.3/37 = 3.5% loss in mileage.
The fuel log is there if anyone want to take a large sample size (or check my math) like say November thru April. That way the city driving factor should get cancelled out a little better, but avoid the warm weather advantage the complete Non-ethanol log has.
Per your logs 2015 annual reports E0 is $0.070/mile, E10 is $0.064 mile. Not much difference but E10's wins at 9.3% cheaper per mile. Not many mods can save 10% per mile.