Depends on the transmission. 1:1 is the breakover between fifth gear and overdrive. Not sure if they have an actual 1:1 whether they call it a fifth gear (or fourth or sixth, however many gears you have) or overdrive or if they can call it either. But if it is over 1:1 it is overdrive, if it is under 1:1 it is a number gear (usually either fourth or fifth).

Higher gear ratio doesn't always make better gas mileage, if you don't have enough power coming from the motor you will end up lugging it and having your foot to the floor all the time and actually get worse fuel mileage. This is why four cylinders generally come with gears a step or two lower than V6 or V8s. Different motors get peak efficiency at different rpms also, there are a lot of factors that affect gas mileage.

How people drive has a big effect on what gas milage they get.
55 on the highway Is optimum here,although no one ever drives at that speed,lol.Also your tires has a noticeable effect on milage also.Drafting behind a big rig will improve your gas milage considerably.