Cody Atkinson and Sean Lawson at the ABC had an article on this topic yesterday. Because it's not behind a paywall, I'm just sharing the link but not the text. Link

Key points are basically that yes a short break does statistically impact performance, and the distribution of short breaks is not even across the competition. We are sort of middle ground for this - 5 games with a shorter break, 3 with even break, and 5 days with a longer break.

Swans have 8 games with a longer break, and Hawks have 8 games where they have a shorter break than their opponent!