They will have alot more acceleration over the stock gears. If you drive normally, not ripping on it, you wont see a decrease in mpg's. You may even see an increase in your fuel mileage in the city. Highway mileage however will drop some. The reason 3.73 are a little too much for forced induction is because they will push you through the rpms too fast to make use of the boost. 3.55s are about as far as you will want to go on a boosted car.