Seeing 315+ H/s on each of my 390x clocked at 1180, though the temp hits 90C. One of the cards occasionally drops out now with 9.1 (was stable on 8 ).. even drops without overclocking. At least the miner resets itself.
Even doing -tt -80 or higher?
Set -ttli 92
You probably should be spending your time looking into undervolting to lower temps, blowing the dust out of your cards, separating them from each other more for better airflow or relocating the rig for more efficient environmental heat removal, reapplying the thermal compound between the heat-sinks and GPU core, etc. There really isn't much difference between 90 and 100% fan speed when in comes to cooling, and you are quickly running out of headroom if you need to run that high to keep your cards at 90C. I have a few rigs with the 390x cards and I know they run hot, but I manage to keep them in the 70C range, I would be worried at 90C.
