Ok so my monitor is an Ultrafine and doesn't have any sort of input for a PC. Also, it would be nice keeping the PC away from the desk. Also also, it would be nice doing productivity work on one computer (my Mac) and just hopping between MacOS and the Remote Desktop. The PC is a 7700k with a GTX 1080 ti. I am using it exclusively for Rhino 3D and VRay. How would the performance be if I were to headlessly connect to the PC via my Mac with -say- an ethernet connection?
The performance of any Remote Desktop connection by the laws of physics and the need to encode the data is always slower than a native display.
So, no, the performance can’t be as good with a remote connection adding latency and delay.
That being said - practically, you are always going to be more productive than getting up and moving to another computer and you can get prodigious amounts of work done remotely across a continent let alone across the room. With a decent WiFi connection (say 802.11 ac and less than 10 radios connected to the AP and low interference / SNR above 10 dB ) or any 100 megabit wired/switched ethernet you will have a hard time measuring the delay or worrying about performance. Gigabit ethernet is even better.
I wouldn’t worry about this performance loss in practice, you are likely going to be 100 to 10000x times slower than the CPU in all cases, not the remote connection.