"auto-fan" : true,
"auto-gpu" : true,
"gpu-threads" : "2",
"gpu-engine" : "1050",
"gpu-fan" : "40-100",
"gpu-memclock" : "1450",
"gpu-powertune" : "50",
"intensity" : "22",
"temp-target" : "90",
"temp-overheat" : "93",
"temp-cutoff" : "97",
"vectors" : "1",
"worksize" : "256",
"lookup-gap" : "2",
"thread-concurrency" : "32768"

+88mV

I'm using this config for both R9 290 and R9 270, 2.2-2.4Mh/s on 290 and 1.1-1.2 on 270.