@David_Bovill I think you should look at using solutions that utilize NDI, it’s worked wonders for me.
I’m using an HDMI output camera (Lumix FZ2500) with a Blackmagic mini Recorder (has both HDMI and SDI inputs).
CPU/GPU usage is significantly lower than when I was using a USB Webcam!
About the original question, I think I would max out the RAM and the VideoCard. I got a MacBookPro with a lower CPU (I7), but 32 GB RAM and the Vega 20. The stability and speed is impressing.
About Camera Input, I tested using 2 Intensity Shuttle (one USB and one Thundeboldt trough adapter 2-> 3), and tested several cameras trough NDI, with iOs NDI app and Spark, both of Newtek. Works fine so far.
And finally, thank you David for the tests with eGPU. I choose a RazorX-eGPU enclosure to be able to change the graphic cards, but well, have to get them to start testing it…