A lot of this comes more from experience than from theory.
In very general terms, the lower the gear (higher numerically) the greater the torque multiplication but also the lower the top speed. For the sake of discussion, you will get better acceleration from 4.00:1 final drive gears than you will from 3.00:1 final drive gears. Accelaration will be even better with 5.00:1 final drive gears, but you may need to shift through three or four gears just to get across the street.
If you have enough horsepower, your top speed will be higher with 3.00:1 final drive gears than with 4.00:1 final drive gears. If the gears are too tall (too high, or low numerically) you will run out of horsepower long before you reach engine red line.
A lot of gear selection has to do with matching the power curve of the engine with driving conditions. sometimes even a slight change in gearing can make a big difference in having the engine in it's best part of the power band accelerating out of a curve on the track. That is where experience and experimentation comes in.
This should get your discussion going.
