Thanks doktor83!

Your rom allowed 4x Sapphire Nitro 480 8GB reach 29.3MH/s (Micron).

I tweaked the settings a bit, but I mostly needed the straps as PBE wouldn't work.

1100 GPU/1000 mV
2050 Memory/1000 mV

Fan minimum 50% makes them run smooth.

I can't confirm his rom is best, but at least the straps are changed. What strap mod did you perform?