I had successfully run 7x RX480 8GB on Z97 Gaming 5. I use older driver like 16.9.2 or tried 16.11.x. Set at bios, 8x4x4x, Gen 1.
Extra thing I did was using Window Testing mode on by below step:
Open Command Prompt , enter bcdedit.exe -set loadoptions DISABLE_INTEGRITY_CHECKS and press Enter. Then enter bcdedit.exe -set TESTSIGNING ON and press Enter.
Hope this help.
that's interesting, never done the testing mode, I shall try that tonight. I have tried the older driver before I tried then new driver, I was only getting 18Mhs on 4 cards. the latest driver runs at 25Mhs on 4.