OK, lets look at this a little more closely.
When I first started on the Lockheed TriStar (-200 series, RB.211-524B02 engines), the aircraft were equipped with the first truly successful FMS in airline service, coupled to three ISS units, for navigation.
As is usual with FMS, the takeoff weight (mass for you European folks
)
was entered (among other parameters) and the takeoff was calculated using the deepest engine de-rate possible, consistant the the runway analysis chart.
After takeoff, and once climb thrust was set, the FMS was engaged in three modes, LNAV, VNAV, and thrust management. The climb IAS (once above 10,000 feet/FL100) was always...min cost.
The thrust selected for climb by the FMS was always the least, considering the weight and climb rate.
Once the ROC decreased to 650 ft/min for thirty seconds, the FMS selected the next higher climb thrust, and this continued to top of climb.
These selected (auto) modes of thrust for takeoff and climb always, without exception produced the LEAST climb enroute fuel consumption.
Of course, we should not be surprised by all this, after all, LOCKHEED did it FIRST with wide-body aircraft.
Ahhhh...Lockheed, a truly remarkable aeroplane