Edit: Last night I found the solution. I hadn't installed the proper [Suspicious link removed]pute driver from AMD (17.30). All cards are now running 28.5+ without overclocking.
First of all, love the program, so many thanks to the developer! Now on to the cry for help
To make it short, I've had a rig running two Gigabyte Gaming 8GB RX580's for a while now and I'm getting a stable 24.5 Mh/s out of each. I do mod the BIOSs using the One Click method on the current Polaris software, I've changed the VRAM to 16GB, and I try to overclock using MSI Afterburner a bit, though I feel like I'm not very good at it. Hash rate's not super hot, but for the moment I'm content.
I recently added on a Sapphire Nitro+ 8GB RX580, which I know some get 30+ Mh/s out of, hoping to get the same result as other posters. After much dinking around, modding the BIOS (both of them), switching BIOSs, and attempts at overclocking, I'm managing to get a measly 18.4 Mh/s out of the card (even mining with that card solo), which is extremely disappointing. So my question is: why is a verified bad ass card so much worse than my other cards, and what can I do to improve? All help is appreciated!
One thing I did not do is install any extra drivers after adding the Sapphire. I figured using the AMD drivers I already had for my previous 580's would suffice, but I may be entirely wrong.
My rig, in case it helps:
Windows 10 Home OS
Asus B250 Mining Expert MOBO
2x Gigabyte Gaming 8GB RX580s on PCIE x1 risers
1x Sapphire Nitro+ 8GB RX580 on PCIE x1 riser
Thanks!