http://www.techspot.com/review/1393-radeon-rx-580-vs-geforce-gtx-1060/
TL;DR RX 580 comes out 2-3% ahead of the GTX 1060, which comes out 2-3% ahead of the RX 480. 9gbps vram makes very little difference for the GTX 1060, and the RX 580 requires 60% more power draw for it's 2-3% advantage. No overclocking was tested.
As I've personally argued for the past several months, you can't go wrong with either choice between the cards in question. Each has its own strengths and weaknesses, but by and large perform about the same outside of 4-5 outliers.
TL;DR RX 580 comes out 2-3% ahead of the GTX 1060, which comes out 2-3% ahead of the RX 480. 9gbps vram makes very little difference for the GTX 1060, and the RX 580 requires 60% more power draw for it's 2-3% advantage. No overclocking was tested.
As I've personally argued for the past several months, you can't go wrong with either choice between the cards in question. Each has its own strengths and weaknesses, but by and large perform about the same outside of 4-5 outliers.