[Ethereum] Which GPU for ethOS

UPDATE: The problem was with the drivers. I got the latest ATI drivers (Crimson 13.2 hotfix for windows) that solved the problem. I'm getting ~21MH/s per card.

I had exactly the same issue on my Sapphire RX580 Nitro+ 8GB cards on the latest Ethos. I expected the stock BIOS to achieve 24-25MH/s, but instead got only 18MH/s on the quiet BIOS or 20MH/s on the Boost BIOS (via card BIOS switch). After some investigation I found that (using the Boost BIOS) lowering the core and mem clocks to spec rates (1257Mhz core, 2000MHz mem) actually improved it slightly to 21MH/s, but no where near to 25MH/s. I then did a VBIOS mod copying the 1750 memory timing strap to 2000 and 2250 entries and now I can run the cards at the advertised boost rate (as sold by Sapphire) of 1340Mhz core and 2100MHz mem with slightly over 25MH/s per card. Note that I switched from the default ethminer to claymore to gain a few percent. Feel free to contact me if you want to try to replicate these steps.