Hot Hardware published a review on the AMD Radeon RX 580 And RX 570 Mainstream GPUs: High Performance Polaris A quote from the article:

In preparation for the impending launch of AMD's next-generation Vega GPU architecture, which will eventually reside at the top of the company's graphics product stack, AMD is refreshing its mainstream graphics card line-up with some more-powerful Polaris-based offerings. In time, the new Radeon RX 580, RX 570, RX 560, and RX 550 cards launching today will supplant all of the current-generation Radeon RX 400-series cards, though these new cards are not radically different from their predecessors. Their clocks, shader counts, and memory configurations have been tweaked, but they?re still based on the same Polaris architecture and offer similar feature sets.

We?ve got the two premium cards in the lineup on hand for testing: the Radeon RX 580 and Radeon RX 570. In particular, we have the MSI Radeon RX 580 and RX 570 Gaming X in-house, both of which are customized and factory overclocked...

 AMD Radeon RX 580 And RX 570 Mainstream GPU Reviews: High Performance Polaris @ HotHardware