Hi Sam,
I am very encouraged to hear you say that you do not think gigabit ethernet is needed. I would certainly bow to your wisdom here and would prefer to use the built in port despite having bought the USB adapter.
However, the reason I assumed I needed the adapter was post 2 in this thread:
where @fzinken says “Any file above 86Mbit average bandwidth will not be able to be played via Ethernet unless you get a USB Gigabit dongle”
One of the first UHDs I ripped was The Hitmans Bodyguard. Running media-info on the resulting m2ts, the average bitrate is reported as 89.5Mb/s, which is of course above the 86 threshold mentioned above. So straight up I thought I had a film which would not work over the built in ethernet port. I guess I have misunderstood something though…
General
ID : 0 (0x0)
Complete name : The Hitmans Bodyguard (2017)/The Hitmans Bodyguard (2017).m2ts
Format : BDAV
Format/Info : Blu-ray Video
File size : 74.0 GiB
Duration : 1 h 58 min
Overall bit rate mode : Variable
Overall bit rate : 89.5 Mb/s
Maximum Overall bit rate : 109 Mb/s