I am having issue, with my rig, I can't get more that 16 Mh/s on my GPUs, and i have not cloud what to do, I read the post here and see that each GPUs should be at least around 25Mh/s.
Mine setup is
4 XFX AMD R580 black edition with driver version 23.20
User the latest drivers from AMD.
Adrenalin Edition 18.1.1 - http://support.amd.com/en-us/download/desktop?os=Windows%2010%20-%2064
Make sure you go into the AMD settings tool and set your video cards to "compute" not "graphics"...