I don't know if it is, but I did every step you detailed for the SSDT-CPUPM.aml (just not the slide calculation for AptioMemoryFix, didn't get it). I just tried with one display connected to one GPU, and I get much better results indeed, but I'd rather have my two displays connected both in HDMI on each GPU…
Nope it's connected to SATA II, and it shows up now with only one display on one GPU!
Yep I did on Ubuntu, but now nothing shows up, no need for a screen, there's just "No PCI Ethernet card…"
Thanks a lot for the advice, it's apparently 2GPU-related for the most part (any idea of why?), just this ethernet that worked flawlessly until now…