318 or 360

All else being equal, how does the mileage of a 318 compared to a 360?
Equally in a truck pulling the same weight trailor, the 360 will get better MPG. In a Duster in 2bbl form, the 318 will get better MPG. Right now, I cannot tell any noticeable difference between my 360 Duster and my 318 Duster for MPG. I've not checked neither