ATTENTION ATTENTION
You will not be able to make GTX1060 work, there are no drivers available.
GTX 970 would work up to High Sierra after that ..nope( i have one I was about to put on Kijiji)
GTX 760 will work out-of-the-box in just about anything until Mojave 10.14.6
GTX1000 or 2000 series will not work at all
Will work in 10.13.4 and above
AMD RX570,RX580
AMD Vega 56,64
AMD Vega 64
AMD WX7100,WX9100
Will work in Catalina 10.15.2 and above
RX 5700 XT
Any reason why you want to pretend to be a MacPro3,1 ? ..it is a lonely island. Everyone is either a iMac13,2 (dGPU) or a MacMini6,2 (iGPU)
Answers to your questions :
1) It is a very good proven ROM for El Capitan
2) Not really, Ozmosis is still stable even tough there has been no new development on it for quite some time. Al new development is on OpenCore
3) No
4) XMAX-E -> Will install as MacPro3,1 if no Defaults.plist found. OC firendly -> You have to provide a config.plist file.
Nvram:
1) Yes or just hold Command-Option-P-R when powering up (with Oz or OC firmware).
2) Yes
3) Yes for Ozmosis (Opencore has nothing baked in)
Tu peux me demander en français anytime