This seems to contradict several other reviews I’ve seen, which show the 7840u beating Intel in all efficiency metrics.

Three sources where efficiency and better battery life are reported for AMD across the board: Notebookcheck, Just Josh (most comprehensive comparisons IMO), and techradar.

Kind of interesting.

EDIT: It appears Ars made a mistake in their review, which explains why other reviewers had different results: https://old.reddit.com/r/framework/comments/16ytxjd/saved_you_a_click_16x_better_battery_life_if_you/k3ar79v/?context=3