the power consumption is really very high
all rx580 cards can be undervolt to get 30 mhs for 75 to 80w per card
try reducing core and core voltage
it will reduce the power a lot
less power consumption lower temps
The RX580 won't get 80Watts @ 30MH/s. The absolute best would maybe be about 120 Watts. When you measure power consumption you need to actually use a watt meter and not the figure that you see in GPU-z. That figure refers to the GPU wattage consumption and doesn't include the consumption used by the memory controller and other parts of the GPU.
I think the best figure I ever got was like 120 Watts @ 27.5 MH/s and this was with the highest ASIC quality GPU i had. Going any lower wasn't possible because it got freezing issues.
So if you got a 6 GPU rig then what you should expect is about ~750 Watts about 120Watts per GPU and 30 Watts or so for the memory, CPU, motherboard, etc.
Yes RX580 is more power hungry then RX570, my best performance rig for 6xRX580 is 710w at 188mh. Lot depends also from card,memory and BIOS modification, like the sapphire Nitros and MSI gaming uses the least power.