Hey Andrasz,
Fuel burn goes almost exponential for ultra long haul ops.
As I recall it, the extra burn per ton for B744 SYD-DFW was about 650Kg/ton uplifted. That refers to fuel or payload coz fuel is really just house bricks until you burn it. Hence it is way more fuel efficient to make a stop at the half way point. Think about covering a tempo T/Z at DFW ex SYD, about 8 tons.
One day the greenies will wake up to this and go nuts about ultra long haul.