Once you exceed Long range cruise which is higher with a head wind (LRC) you pay a penalty in wasted fuel. Max continuous which means what it says is certainly faster but is excessive for the head wind experienced, i suggest. Max power she surely would not use ,in view of the consumption and engine stress. I haven't followed the arithmetic apart from a simple howgosit . But i suggest theres possibly an error in the earlier assumed position reports.Instead of Z there was use of local time(standard time for location) which certainly led to confusion with radio skeds. Her lapsed time to the Howland vicinity was 20 plus hours.
I can only relate to my experience. but excessive thrust means you wont make the destination. Early days for me there was little emphasis on cost. The fuel uplift was sufficient but anything approaching Max continuous i would not have reached my destination.