Not sure what to say gents, don't doubt you're right technically, but having watched 4 x 4k HDR films this past week, smallest being 40GB, largest bring 60GB (2h 40 runtime which puts me under the 100mbps ceiling I guess) I can hand on heart say it's not stuttered once in any of them... If it can do that on 100mb port then it's spec'd A-OK in my book. No need to use a device (my NUC is connected to the TV is I wanted to use it, but I don't use it as the TV client is so good).
Prior to this thread (what prompted me to post it) I was getting pauses every 10mins or so. I must've had a stupid string that I've resolved in the Plex server or something.
Something has changed, but the only thing that hasn't is the hardware. Sorry I can't give you more detail...