I have an ASRock H81 BTC R2.0 and 6 MSI RX 470 Gaming GPUs
Up to three GPUs everything runs smooth.
If I put in #4 I get all kinds of errors... BSODs, Code 12 or 43.
I changed risers, power leads, PCI-E slots and GPUs to no avail.
All risers connected with SATA-Power, PCI-E slots extra powered with 2 4-pin molex plugs from PSU as stated by the MB manual.