I recently upgraded the flash drives in each of my rigs to SimpleMiningOS-NV-RX-v1176-4.17.1-amd18.10 which updated the Linux kernel to 4.17.1-smos, so I figured I'd play around with the overclocks. At this point the only adjustment that seems to be stable is a slight power limit decrease. Normally I run each card at 100 watts, but since the image upgrade, I'm running them at 98 watts. It's only a 2 watt difference per card, but across my entire farm it adds up.
The smOS overclock settings above are for Asus GTX 1070 Turbo mining Ether at 31.3 MH/s (stable) with ethminer-v0.14.0.