Isn't 5th on a manual a higher gear than 4th on an auto?
Anyway, don't forget that your tire type and size plays a big roll. There are two things to consider. First, if the overall diameter is larger than stock, your odometer will be reporting fewer miles traveled. Second, if you are running a wider tire there is more friction (good for racing bad for mileage).
If you're really worried about mileage you can pick up a set of 16x5.5" wheels and some 175/55/16 tires. That will make a big difference.
Anyway, don't forget that your tire type and size plays a big roll. There are two things to consider. First, if the overall diameter is larger than stock, your odometer will be reporting fewer miles traveled. Second, if you are running a wider tire there is more friction (good for racing bad for mileage).
If you're really worried about mileage you can pick up a set of 16x5.5" wheels and some 175/55/16 tires. That will make a big difference.