I did try it, the syntax of the PCI port was kinda confusing, since in most other places they use colons instead of underscores (and the amount of digits was different), but none of the parameters seem to have any effect in wayland.
Your link refers to the other problem I had, which has since been resolved with a driver update:
…from that angle, it’s starting to look like I just have to wait for someone who can actually do it, to make multi-GPU setups work actually, not just technically
