I'm getting 30 -31 Mh/s per card on my 8 x RX580 Sapphire Nitro+. Rig pulls about 1450 Watts. See the video below if you have been trying to get them to run at 30 Mh/s with improved power consumption. If you still have questions let me know.

https://www.youtube.com/watch?v=8clkIopKZ-Q&t=1s