The 787 has less sweep than the 747, A380, and A350.
It has significantly greater wing sweep than the A330/A340 which is the M0.81 types that I was referring to.
Without going into all the technical aspects, it is essential that aircraft used for ULR services must cruise at higher speeds for passenger comfort reasons as well as crew duty reasons. On some of the sectors that have been discussed, it wouldn't take much of a technical delay before the crew duty limits come into play.