If they are around the same price it is the RX500 series uses a refined Polaris chip and also seems to include a newer memory state that allows for lower power consumption when watching videos and using multiple monitors (same resolution)
It depends. RX 400 series cards are going on sale quite frequently, you'll see RX 480 8GB's drop below 200 dollars. In that case the 400 series will provide better value for the money. Base price wise the RX 500 series is the better option.
It depends. RX 400 series cards are going on sale quite frequently, you'll see RX 480 8GB's drop below 200 dollars. In that case the 400 series will provide better value for the money. Base price wise the RX 500 series is the better option.
The 580 and 570 are overclocked 480 and 470 cards. So you cannot expect any overclocking headroom in them. GTX 1060 overclocked to 2000 MHZ+ on core will be better (in most cases) or equal to a RX 580.