I'm in south Jersey and I commute to Delaware everyday. It's 90% highway. It's the best commute I've had in years.
Mobil 1 0w40 is arguably Mobil's best oil. It's designed around racing and high performance engines. For whatever reason, people always seem to forget that you can technically use any viscosity in any engine without causing any problems.
Low viscosity oils, 8 to 10 speed transmissions, CVT's etc...are all about increasing fuel economy.
The extra viscosity is what I would want regardless because of fuel dilution. It makes sense.
The 0w40 is also using a slightly higher class of base oils and entirely different additive system.
2014 Mazda 3 S GT AT - OE oil
2003 Forester XS 5spd - M1 0w40