IIRC a 747 burns about 4000 gal at cruise, industry average occupancy rates 60%(?)... My GMC Suburban 350 ci gas will average 20 mpg @ 60 mph with 100% occupancy (the dogs get a seat each!) We averaged 19.7 Alaska and back.
Do you have any data on your speculation?
If you ran your GMC truck at 500mph your fuel use would exceed the 747s. The cost per passenger mile of a 747 going at 500mph is lower than the cost to operate an automobile at 50mph.