The Boeing B744 Data manual quotes an average saving of 1800 lbs of fuel from brake release to TOC by accelerating to Econ Climb asap after cleanup, as opposed to 250 to 10,0000. At high weight Econ Climb (Cost index 100) may be 350 knots. I have compared fuel to flight plan at TOC, and this prediction is accurate. Climbing at best ROC (approx 310 at high weight) doesn't make any improvement.
