If you decided to jump in to miming thing.. and picked up ETH or ethash algo coins, one of the cards you should consider is Gigabyte Aours RX580, for this post I can give you bios mod for Aorus 4 GB version with elpida memory. Power usage with this bios mod is arround 100w per card, with hash od 29 Mh per card. Different memory type can give you 30 Mh per card, but I guess luck was not on my side this time so I got elpida version. Anyway considering that this card with stock bios giving 24Mh per card with usage over 200w this bios mod is really great. After moding and also undervolting it shows much better performance for mining. In this bios mod default gpu and memclock are set to 1085/2000 and you can alos set -96 core voltage in your afterburner couse in the bios mod core voltage is set to 925. If you have electrical problems or u are using cheap and unstable power supply, rig can be unstable if you turn core voltage down.
Here is what i get in windows 10 with claymore 10 miner:
And here is bios mod you can try:
Gigabyte Aorus rx580 4gb Elpida
Gigabyte Aorus RX 580 AMD Radeon 4 GB