Add the padoka repository for more up to date mesa drivers. Amdgpu-pro isn't really for games, it's for professionals (who need the open-cl performance). The open source drivers have more than caught up by now also. btw, uninstall amdgpu-pro with
The non-pro drivers should be installed by default, check with
lspci -k |grep amdgpu and for the 480 it should already be telling you amdgpu is in use. (There is a chance it might end up using the older open source radeon, but I highly doubt it. If you don't see the kernel driver in use line listed, that is probably the case )
Padoka repo https://launchpad.net/~paulo-miguel-dias/+archive/ubuntu/pkppa/
There was also one other up to date mesa repository people recommend, but I don't remember what it is called off hand.