CX,
It would burn about 60t more than a 777 to LHR and 50t more on the return. 17t freight on the long range ones with 489 pax. 19t on the med range ones with 517 pax. Think I showed previously how the extra pax ticket cost covers more than the fuel cost. Unless of course fuel gets to over $4000 per 1000kg.
But if you haven't got the pax base to fill em you wouldn't want to be flying them. ULR flying from the sand pit is being moved from the 777 to the 380 as it makes more money. Our 777s have 54 more seats than yours. They become MTOW limited at 12hrs so are only carrying 45t of revenue to/from the oz east coast and less to LAX.
The Don.