Tried this a bit ago with the Sapphire 480. Had to return that because of shart fans. Now I have the XFX. I am reluctant to install AMDGPU-PRO through Yaourt. Last time I tried with the Sapphire it messed everything up badly enoughl where I just wiped the system.
I must just be a glutton for punishment because I could have replaced the Sapphire 480 with an Nvid.
Something something "everytime I try to install the AMD proprietary drivers on an Arch based distro, I have issues because it's a rolling release OS."
Specifically, last time I tried, AMDGPU-PRO required Xorg <1.18. But since the latest Xorg package available on Arch at the time was 1.19 or greater I couldn't do that without downgrading it. But downgrading Xorg means downgrading other dependencies and then I got stuck in some dependency hell where I couldn't uninstall a package because it depended on itself. There were like 3 or 4 packages that ended up this way.
I'm sure it's possible. But I'm sure I'm not yet capable to make it happen, and the wiki didn't help.
So I went "I guess I'm not doing that." and reinstalled the OS.
.... I really should start using my backups instead of reinstalling every time.
But yeah, maintaining all the older versions of the packages I would have to downgrade by preventing their upgrades while allowing other upgrades would be annoying.