ok so (and apologies for hijacking this thread).
Screenshots here:
https://forums.overclockers.co.uk/threads/sapphire-amd-deals.18974942/post-36543548
I tried several games, Fallout 4, Fallout 76, Days Gone, Rocket League, Kerbal Space Program, Mechwarrior 5 Mercenaries, all run pretty terribly.
The artificating shown was one start up a few times, then gone after a restart, then again after closing a game, so wasn't constant, leading me to believe that wasnt a cable/monitor problem. I also have a video of the GPU plugged into the system with the screen aritficats like that.
There were no artifcats as such in game, but all games running terribly, input lag, low FPS, some glitching like the windows mouse loading icon in screen.
I checked the GPU was seated correctly, and firmly in the port with the "click" checked both 8pin power connecters in firmly, using seperate cables from a corsair 850w psu. Good quality DP cable used. Old nvidia drivers wiped using DDU and new AMD drivers installed fresh without the internet connected so to avoid windows trying to its own "universal graphics driver" or similar.
This was installed on otherwise working PC which has been sold, with a current 3070 working fine, no other hardware changed.