Here I took some tests with an HPX170. The stills were exported directly from Premiere. Then, I compared in Photoshop and this is what I found:
When expanded, 720 footage looks softer than 1080 footage.
Is for the extra resolution?
To answer that I added an Unsharp Mask filter to the 720 expanded footage and it looks exactly the same as the 1080 footage.
My conclusion is that for the HPX170 there’s no real benefit for the quality of the image when shooting at 1080. You only end with bigger files.
I hope this helps
—————–Real 720———————

—————–Expanded 720—————–

—————–1080 footage—————–

—————–720 with Unsharp Mask——–

PS. I have just realized how personal this footage is.