I think the reason that they are going for the very high cruise numbers is so that they can cruise it HIGH without losing time.
Get above 37000 and you start to take some steep groundspeed penalties. To make it up they got to get to a higher mach number. If they can get the higher mach number at the high altitude, they will get multiple benefits, not the least of which is the ability to go DIRECT. They would forexample get above the organzied track systems etc...
I think the emphasis on this aircraft is actually getting high, not fast. Fast is a byproduct to make the aircraft fit within accpetable scheduling guidelines. If they stayed at .80 and stepped up into the mid 40s the aircraft would be crawling over the ground...
Getting high lets em climb over the jetstream as well, furthering their advantage in the winter going west...
Cheers
Bohica