Brand: just OEM AMD, not a particular brand, because I bought it as part of an Apple Developer Kit for Thunderbolt 3 eGPU
Performance: At 1080p60 it'll play modern games just fine. Super high end games like Unreal Engine 4 games will probably have to run on medium detail, but MMOs, etc. can run at max settings no problem and the framerate will be very smooth.
Pick 1660 Ti over it: The 1660 TI is $80 USD more than the RX 580, uses less power and delivers significantly higher performance (see: https://www.videocardbenchmark.net/compare/GeForce-GTX-1660-Ti-vs-Radeon-RX-580/4045vs3736 ) so I'd …