OK, I think that I'm getting it now. Using the B744 numbers given, in RVSM airspace, burning 10-11 tonnes/hr you could climb to another level (2000') every two hours. This could mean a number of altitude changes during say a JFK-EGLL trip.
I have some archived flight data, and after questioning a controller who worked Gander Oceanic, he says that by time the flights were passed from New York ARTCC, they were all level at their final altitudes. This, based on previous posts, would this be due to the aircraft NOT being at their MTOW when departing? So, for the longer range types (ER's) are the tanks always full for a transatlantic flight or just enough fuel to satisfy the flight planning requirements? Can I deduce that if a B777-300ER can fly for 15 hours then for a 6-8 hour flight eastbound over the atlantic, the tanks are maybe half full????