Originally Posted by DataJunkie

Generally, you will use whatever front chainring \ rear cog combo that enables you to hit the cadence you are shooting for. However, if you can pull 100 in the big ring small cog combo then you are really hauling.
Basically, you disregard speed and train your legs for a higher cadence. Then you start working on power by moving up in gear.
Consequently, a high cadence in a high gear will enable you to keep up (generally). Focus on staying in a high cadence first.