Hello Mike,
HD is
not what I would call a lot of data, even at 60 fps.
You were mentioning the machine can struggle already, but you could also look at the memory usage when you have your stress situation and who is consuming that memory via Task Manager.
From what I can see, the Opal and Ruby reference systems advised by the software vendor for HD both are dual-channel, because it makes sense.
But I can confirm that no pixel comes free of computation.
The USB-C DisplayPort Alternate-Mode (Alt-Mode) "USB" display is directly driven by the GPU. There's no encoding over USB or things like that (because they are not really USB) and this is the reason why, for instance, they cannot be connected through USB hubs. It still consumes GPU though.
I think there is a confusion about technologies and protocol. The USB-C plug itself does not mean the transport is USB traffic. I could simplify what "Alt-Mode" means by "Not USB traffic over the USB-C plug". It requires specific hardware on the platform, on top of USB.
We've been
fitting HD on USB 2.0 with 10y old machines.
Kind regards,
Alban