Originally Posted by TMonk

Your speeds won't change that dramatically, but they will a little. It's not like you will suddenly be able to produce more power, and you certainly aren't any more aero or light with a geared bike, so those speed ranges you posted above still apply.

What you'll learn is that there is a (small) variation in power over a given time period, with respect to cadence. The ability to hit those sweet spot cadences, and hold them, is what will make a difference over the long haul.