That said, speaking as a guy who's flown the 7ER, 73N and 320, it is nice to be able to comfortably climb above weather in the 7ER that I would be getting beat up in waiting to get lighter in the 321.

Or being able to meaningfully impact arrival time without riding right at the overspeed warning.

757 has a much wider mach band it's happy in at normal operating weights. Planned for cost index 40? Crazy EDCT or deice delays? 80 or 100 will usual shave a good chunk of that off on a transcon while still being able to land above planned fuel. 757 doesn't seem to really get crazy with the gas burn until you go above .81

But its also happy flying at CI 0, down at .74.