The media wording about the increased speed and fuel usage is particularly bad.
The original explanation of the latest new crash position calculation, that I believe, explains the reduced distance travelled - is that the aircraft initially used more fuel than originally estimated, because revised calculations of the flight path, speed and height, in the sector between where the aircraft initially diverted from its flight plan, to the point where it was last sighted on radar, showed an increased fuel burn over initial calculations.
This then left less fuel to burn between last radar sighting point, and fuel starvation point. The new calculations obviously pick up increased flight phugoid movements or perhaps even throttle position changes.
Spare a thought for those doing the calculations, with so little real information from the flight deck.