We bought a new
2015 mazda 6 sport with the manual shift a few months ago and just got done with our second road trip.
The car is as delivered with the tires at the max of 50 psi instead of the recommended 45psi, and all I did otherwise is use the cruise control set right at the 70 mph limit, and the car again got just over 40 mpg for the trip.
Most of the time the econ gauge is hovering in the low 40's, slight uphills drop it into the low thirties, bigger hills into lower 20's, but on the backside of the hills mileage will often jump into the sixties or even 70's. It makes you really notice hills.
Around town my wife is averaging about 30mpg most of the time which is pretty good for her 5 mile all city commute.
According to mazda the car has a low Cd of 0.26, and the gearing is pretty tall in 6th, about 2200 rpm at 60 mph. The result is an effortless 40 mpg hwy, and I suspect you could do much better yet by hypermiling it.
Dean