I am currently running El Capitan on a MacPro 2012 with an NVIDIA GeForce GTX680 graphics card and it's working fine. When I installed High Sierra the graphics went haywire. This set up has been OK till now when the CAD software I use (Vectorworks) issued the latest update which proves to be a bit buggy with El Capitan. Which graphics card should I get to overcome this problem? I'm thinking of a Sapphire Pulse RX 580 with 8gb of RAM. I've attached a copy of the system overview.