Recommended performance speeds are often a compromise compared to the true optimum speeds. A few points to consider:
Mach number is the speed parameter relevant to range and endurance theory. Any quoted IAS is calculated from the required Mach number.
Going back to the original thread, in a drift down situation with one or more engines inoperative, the drag will be different (usually greater) than in an AEO hold.
When holding, you do not want a small speed reduction to put you on the backside of the drag curve and have to make a large power increase to recover the situation. Also, you need to maintain an adequate margin above the stall. Note that there is no relationship between stall speed and min drag speed.
Much of this has been said before - just a different way of putting it with a few new thoughts.