The default A320NEO is able to defy the laws of physics with a record breaking fuel consumption of just 1230kg/hr at 375KTAS 320KIAS FL100. This is all with a payload of 14.5tons.
This is in fact even more miles per gallon than at FL390 with 250KIAS, so there is little point in even climbing. If only this was true in real life we’d see fully loaded low-flying A320NEOs flying London to Singapore nonstop and other such pie-in-the-sky madness.
Look at 22:56 