hand calculated my 05 with a 5 speed will give me 28mpg on the freeway and mixed i get about 20mpg ..

id keep the car ya have too... but thats just me

 

Don't forget that since 2011 the 6 banger has a 6 spd tranny.
This is how Ford got a better gas mileage really, lowering the rpm.
The .3 difference between the 2 engines by itself didn't get you there.

Stay with what you have for now since your gains won't be all that much.
Numbers posted by the manufacturer are never spot on...