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It's actually easier with your RX 480, since it already has it's device ID in the framebuffer kext, thus it'll load, just without acceleration. A non-EFI Maxwell GPU won't give anything but a black screen in OS X until the drivers are installed, so you need a 2nd GPU or install the drivers through VNC.

At least Apples drivers don't crash any longer with a Maxwell GPU installed, they just won't do anything.
 
Thanks for answering so quickly—before I deleted the post!! =)

I could have an old Nvidia GT120 installed as a second card as it's only single width and just hook the monitor up to that...

But it sounds like 980 Ti on Sierra is same as on El Cap? It works with already released web drivers?
 
Web Drivers release is fairly predictable but one needs to be cautious before doing any system updates. RX 480 is not maintenance free but it's less of a hassle.

With that said, the 980 Ti is the second most powerful GPU you can use on Mac OS atm.
 
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