FYI - latest eXtremal kernel and params utterly crash my AMD systems over a period of time. About half drop to 0 Sol/sec and the other half become unresponsive and require hard AC cycle.
It also won't function at all on gtx970.
More memory intensive kernel, if you have VDROP+ modded bios some cards are not able to handle it well.
Two of my RX 480 are behaving very good, but the other two constantly crash. Although the cards are the same "Sapphire Nitro RX480 8GB OC" they had different bios revisions. I bought them in pairs so the first pair seems to handle vdrop+ bios but second is crashing. Even with unmodded bios cards do 95S/s vs 105S/s for modded.