Typical TOW from LAX would be 350T, MTOW is 396T, MLW is 285T so you'd be looking at at least 30 mins of fuel dumping to get down to MLW. Northern Canada and the Atlantic are rather flat. The only significant terrain en route is over Greenland where the MSAs are of the order of 17000 ft. By the time the aicraft reached Greenland from LA it would be at a gross weight of around 300T. Even at temperatures of ISA +20 (which you ain't gonna get over Greenland) the the 2 engine driftdown altitude is 21000ft. Once the terrain is no longer critical the Long Range Cruise altitude is around 19000ft and LRC speed is a healthy M0.68. Stacks of spare performance.