I recently picked up 2 Gigabyte Gaming RX 570's. They're in 2 different machines. I haven't done anything special to them yet as I just wanted to get them in stock. Here's my results thus far:

GPU0 t=72C fan=30%
ZEC - Total Speed: 280.034 H/s
ZEC: GPU0 280.034 H/s

It's the same on both machines. Using Claymore 12.4.