My friends and i have three rigs running, two with 8 Radeon RX 580 8 GB and one with 7 Radeon RX 460's 4 GB cards (i have a few posts about our rig). My friend has been managing the rigs and found that they were very unstable at times and sometimes i would log into the pool at night and see they were down, which was frustrating.
After troubleshooting, he discovered 4 of our 8 GB cards (all the red crimson type, none of the black fans) were causing the entire rigs to go down thus he removed them and he redid the bios on them. They still are not running well thus we have left them off the rig till he can figure it out and now we have three beautiful rigs running great. Here is the rigs action now:
Nice, were they BIOS modded or overclocked when they were unstable?
My friend personally modded the BIOS so he was going to go back in and redo it and see if he could tweak some things. It may turn out to be a component we bought off ebay though.
We got some new PCI-E 4X Female To NGFF M.2 M Key Male Adapter Power Cable Converter Cards (ebay title, i can list it if my label doesn't make sense) that had the OC label on them which our others didn't so my friend started to change them out and he said he thinks it was those actually. We use those because it allows us to use all 8 slots on our mother board instead of the 6 that it could normally handle.
Basically the good news for us is if it is this part, then the other cards we have were not the cause of the stability issue. Sucks that a minor part like that can be an issue but now we are even better at trouble shooting our rig so will take the loss of mined coin as a lesson learned cost.
Sorry, i didn't answer the overclocked question but i believe he did not since he was trying for stability. He said he could get each of the 8 GB cards to hash 26-27 MH each but that they were super unstable though that was before the component issue we identified. Hmmmmmm...