I just wanted to chime in with my current hash rates of some of the cards I'm using.

Please note that I haven't really optimized that much, I've only modded the memory straps in the bios' and then underclocked core and overclocked memory with SimpleMining.

6x Sapphire RX 570 Pulse Mini (ITX): 28.10MH/s ETH + 420MH/s SIA. 1500 straps, 1106MHz core clock and 2000MHz memory clock. Have powertune set to 1 in SimpleMining. Hynix memory.
4x Asus RX 570 Expedition OC: 27.15MH/s ETH + 430MH/s SIA. 1500 straps, 1180MHz core clock and 1900MHz memory clock. Have powertune set to 6 in SimpleMining. Elpida memory.

I just set up the 4x Asus cards while I'm waiting for risers to be delivered. I still have 14x more Asus RX 570 Expedition OC and 12x Asus RX 570 Strix Gaming OC to go through but I'm waiting for risers.