Rat 5
I bow to your greater knowledge. I was merely going on my understanding of the basic Boeing CI, which will give climb, cruise and descent speeds to prioritise money over time, or vice-a-versa.
With CI 30 giving a 270 kts idle descent and CI 6 giving 245 kts, one presumes that the earlier TOD and slower idle descent is more efficient in terms of cost. Naturally, without ATC interference and with wholly correct FMC inputs, both would theoretically give an idle descent to the final approach.
Ergo, maintaining high speed below FL100, unless the restriction were removed before TOD, would burn extra fuel.