Were you able to run 7 GPU's on these?
Using powered risers and Linux, they should work fine. Note that I have not used these boards. I bought them with the idea of running 7 RX 470's or 480's.
I have the Asrock H81 and H97 boards and have run 4 cards on MSI GA Z97 4 slot. I might build a rig with one...its tempting.
I would not try to run 7 cards on Windows.
I have these. No issues running 7 x RX480 on them. You just need to edit in the BIOS to make all first three PCI-E section to Gen 1 and for the speed of the 3 x 16X slots to 8/4/4 instead of factory default for the Motherboard to be able to see all 7 slot at 1x for use with your Power Risers.