I've just build my second rig using 8x RX 470 (Samsung) and stock hashrate was like 21Mhs. After using the paid polaris 2.2 (thank you Mattthev) the hashrate increase slightly like 1-2Mhs. Then I adjust clocks (Core 1050 / Mem 1900) and I am getting 27.1Mhs.

If i try to adjust the memory higher like 1950+ the system will crash and restart miner many times, it's not stable. If i adjust mem to like 2000+ I get invalid shares.

Are you still achieving 30+ Mhs on the RX 470 (Samsung) cards?
I downloaded original bios, loaded into the paid Polaris Bios Editor 2.2, patched for power saving OC and applied... saved and loaded the mod bios.

Did I miss something?