Finally found a great gpu! Paid 600 for it but whatever, I needed it. It's a Sapphire Nitro Radeon RX 580 8GB Special Edition. It performs AWESOME! I'm playing NFS Heat at
Apple EFI AMD RX580 4GB and 8GB Sapphire Pulse for Mac Pro 4,1/5,1
SAPPHIRE RX 580 8GB 2048SP Video Card 256Bit GDDR5 Graphics Cards for AMD RX500 series RX580 8GB Cards DisplayPort HDMI DVI Used