In our outfit, A321 v 757, 757 uses ~20% extra fuel for same payload / route, and might save a minute or 2 on timing (up to, say 2:30 legs).
Go further afield, and the 757 starts becoming effective, and the A321 limiting.
Of course the 757 is more fun to fly etc, but the bean counters, Swampy, and the SLF who pay the fares are not really too interested in that
NoD