I am being honest when I say that refiners don't make anywhere near enough MTBE to put in their gasoline. They have to import the stuff from around the world to get enough to make CA gasoline. If you want to look at the racket, look at the politicians. They mandated the use of MTBE, and then blame the refiners for using it. Also, I'm sure they got plenty of money from the corn farmers to have ethanol put back in the gas. Also, I know you've heard it before, but gas is cheap compared to the rest of the world, and what we've paid in the past. Remember, when refiners are doing well, they make about 7 - 10 cpg. In the meantime the goverment adds about 60 cpg in tax. Who's doing the ripping off?
Anyway, this isn't about gas it's about cars. My point is that weather (temp/humidity), elevation, state of the individual car, as well as differences in government mandated specifications of gasoline are what cause the performance differences we are seeing.