Did you mod the bios on the 580s for starters? Elpida memory is not the greatest but you should be able to queeze 26-27 mh with proper setup +driver.
Forget the baseline without mod. Try it out on 1 card
Very first may be try the beta driver from August or the latest one and set to compute mode.
I followed a tutorial on youtube but I'm supposed to have two sets on timings in Polaris... I only have one and theres no :'s - I didn't get any increased anything, can you link me to a bios that I can use? Ill continue looking in the meanwhile
My driver is currently 18.1.1 Crimson all set to computing mode in AMD settings
EDIT: MODDED BIOS but only got to 13.5MH/s ETH and 650H/s XMR and its really jumping back and fourth from 12-13.5 or 600-650