If I may make a couple of brief observations.
As a first approximation, cruise performance is a matter of thrust minus drag. If one approaches the desired cruise speed from below with the book thrust figure, then one would never quite get to the target speed as there is a need for a bit of excess thrust to do so.
Conversely, if the speed is approached from above with the nominated cruise thrust set, then speed will progressively decrease to and, usually, slightly below target speed as the atmospheric bumps and thumps take their toll. It is a bit of a battle on a small scale. Depending on the state of the air mass, this might occur comparatively quickly or slowly. Also the particular drag polar shape will influence the degree to which the effect is seen.
Whether you get into the initial higher speed state by using excess thrust or descending from a slightly higher level is immaterial.
I have always presumed that this phenomenon is what people mean when they refer to "the step" although, clearly, the term is an historical reference to flying boats and planing speedboats and the like as one of our colleagues observed in an earlier post.
I fail to see why it is something which people get excited about. The manufacturer gives us a bunch of numbers for performance and the ops engineers monitor and, if necessary, modify the figures for individual aircraft in line service.
Within the constraints of practical operation, we can probably squeeze a few knots out of the old girl from time to time - but it is a small matter.
Some aircraft, such as the F27, have a quite pronounced "low drag bucket" in the drag curve shape in the region of cruise alpha for all the obvious reasons. The term is quite apt as the curve has such a shape.