In case anyone is trying to figure out the settings for the R9 270X, here are mine:
"powertune" : "20",
"intensity" : "13,13,13",
"api-listen" : true,
"auto-fan" : true,
"gpu-fan" : "20-90",
"gpu-engine" : "1020,1020,1020",
"gpu-memclock" : "1250,1250,1250",
"shaders" : "1280",
"worksize" : "256",
"lookup-gap" : "2",
"thread-concurrency" : "6720,6720,6720",
"temp-cutoff" : "90",
"failover-only" : true,
"temp-target" : "65",
"log" : "5",
"queue" : "0",
"scan-time" : "1",
"expiry" : "1",
"gpu-threads" : "2"
It gives me around 200-210 Kh/s per card
cheers