The DC/DC chip on ethernet controller handles inputs from 5 to 12V. We tested cases of 5V and 12V and both work.

We also tested the temperature using thermal pads and not using. There are only negligible differences. This is why we marked them as optional. On the other hand, the current thermal pad solution may introduce bubbles which worsens the temperature in some local area. So we do no install them by default, but still ship them along in case there is any rare situation when the back of PCB is damaged and becomes conductive.