She would have been about 14500 -15000 lbs . The auw was originally 10500lbs ?. To say in the air for some 35 plus hrs she would need to fly at endurance speed (best L/D plus an increment) . I would suggest this would be in the vicinity of 80-90 kts ,for 4000 miles is 44 plus hrs. She didnt do this she was using a TAS of 140-150mph outbound