with 4 x R9 280X Sapphire Toxic
can u please tell me your OC and are u under voltage or not ??
no OC and no under voltage - just all cards running with stock settings.
the rig is now running fine, almost 3 hours and stable with this hashrate (~1330 h/s)
that's weird have same Gpu but only 3 got only 890 h according to your speed i should get 330 etc 990 Total
How much Ram do you have ??