Both vehicles are identical in every way, they will be travelling at the same speed on the same road. The only difference will be that it is a hot day to be in the four doortruck, so one vehicle has all the windows open and the A/C is off. The second truck has all the windows up but the A/C is on. They both have 5 gallons of gasoline in their tanks. Who will run out of gas first.
Considering mileage, it's strange but my old 1983 Honda Civic 1300FE got better mileage than my 1500 does. I get a laugh at all the folks around here who think the hybrids are a great deal and they don't get the mileage my old Civic did without all the complication and expensive batteries.