As an illustration to my post #49, I thought the following graph might be interesting. It shows the variation of lift-to-drag ratio (L/D) with airspeed.
For example at 1.4 times the minimum drag speed Vmd, the L/D is about 0.8 times the maximum L/D.
The relation is based on a 'parabolic' drag polar and is independent of configuration, weight or aircraft type.
