I bought 5 each of Gigabyte Gaming 580 8gb, Gigabyte Aorus 580 8gb, and Msi 580 Armor 8gb. The Armor cards are absolute junk and I'm sending them back. Modded one of each card and got both Giga versions up to 29mh/s stable, Msi would never go over 26mh/s but mostly stays at 24mh/s and the mod and/or changing core/clocks only makes things worse. TBH I'm thinking about sending all the cards back and waiting on Vega. If these cards had done ~30mh/s they would have almost paid for themselves by the time Vega releases. MSI Armors are going back for sure! Total garbage. Cheap construction, no backplates, just nothing good to say about them.
That's funny, I bought some of the MSI Armor RX580 8 GB as well and I am getting 30.5 Mh/s on each of them mining ETH while drawing about 105 watts/card measured from the wall, GPU-z shows 75-80W. May I ask how you modded them? I simply copied the 1:1750 strap to the 1:2000 and I am running 1125/2275 clocks with 0.900 core voltage. They work just as good as the RX480's, not any better but not really any worse either.