The price difference between E-free and premium is not much more...and I get much better HP and MPG on E-free in my GM LS.
Always hated pre-ignition chatter on even premium, so it was a gift from the hotrod gods when this very liberal state started allowing the highly polluting E-free here.
Plus the long storage of everything else is a bigger bonus, like others have stated.
Trips to Montana are worth the extra cost, climbing all those mountain passes and all.