Undervolting the R9 390s to -30mV and using the parameter: --opencl-launch 24x128, the hashrate reach 15.5 Mh/s (Core Clock 1100, Memory Clock 1500). Temperature around 70c
What is your actual voltage being reported? All of my 390s probably need new thermal paste, I can't overclock and I have to underclock just to have a normal temperature. Also do your cards hold a steady 1100, or does the clock bounce around?