There's over twice as much content in the first test. It's around 3.8gb/s vs 30gb/s if you divide both folder size and both du durations. That makes it 7.9 times faster and I'm comfortable calling this "almost 10 times".

The total size isn't what matters in this case but rather the total number of files/directories that need to be traversed (and their file sizes summed).

oops. I missed the size diff. that's a solid 8x. that's cool!