Yep. Sorry for not making it clear in my post: I understand this, I was merely listing the interface ID's because the "nettop" command output doesn't show the friendly names, it only shows those IDs.

Reading back on the post, I can see how the post makes it look like I might have thought that the ID number was somehow a priority level. Thanks for making sure.

I haven't dug any farther into the problem since discovering, via the "nettop" command, that the backup process was definitely using the ethernet interface. I don't know why it's slower when wifi is enabled, but at least now I know that it's not an interface priority thing.

Thanks!