gas quality

That's a heck of a drop!! Hopefully Vermont follows suit!!

Another factor in the winter is the denser air causes more drag. Ask a pilot how much faster they can climb in winter vs. summer (denser air = faster climb).

I agree that in many areas it is all the same gas except for the additive. True all the way up the east coast, if you've seen the maps of the pipeline on the news since it has had 2 major problems in the last few months. My father had as a customer one of the local gas suppliers so he would be at the fuel depot once in a while. Every brand came in and filled up their tanker truck, and the driver would dump in a bottle of their brand's additive.

From the fueleconomy.gov web site
Ethanol is a renewable, domestically produced alcohol fuel made from plant material, such as corn, sugar cane, or grasses. Using ethanol can reduce oil dependence and greenhouse gas (GHG) emissions. Ethanol fuel use in the U.S. has increased dramatically from about 1.7 billion gallons in 2001 to about 13.4 billion in 2014.1

E10 and E15
Most of the gasoline sold in the U.S. contains up to 10% ethanol—the amount varies by region. All automakers approve blends up to E10 in their gasoline vehicles.
As of 2011, EPA began allowing the use of E15 in model year 2001 and newer gasoline vehicles. Pumps dispensing E15 must be labeled. A vehicle's owner manual may indicate the maximum ethanol content recommended for it by the automaker.
Ethanol contains about one-third less energy than gasoline. So, vehicles will typically go 3% to 4% fewer miles per gallon on E10 and 4% to 5% fewer on E15 than on 100% gasoline.