"I’m not sure why the efficiency difference with the 777. My guesses from the economics viewpoint are that the weight difference has to be one factor – it weighs a lot more than the same capacity Airbus."
Of course if you want to fly non-stop from say HKG to JFK, the 772ER will do it while the A333 will not. The extra weight at the same capacity does produce a tangible benefit in terms of payload-range.