Averaging around 480 Kh/s with a Sapphire R9 270x, seems to be the most I can squeeze out of it...

My setting for anyone interested:

"api-listen" : true,
"intensity" : "19",
"vectors" : "1",
"worksize" : "256",
"kernel" : "scrypt",
"auto-fan" : true,
"temp-cutoff" : "85",
"temp-overheat" : "75",
"temp-target" : "70",
"scrypt" : true,
"thread-concurrency" : "15508",
"gpu-thread" : "1",
"gpu-engine" : "1135",
"lookup-gap" : "2",
"gpu-powertune" : "0",
"gpu-memclock" : "1500"