Someone who can share good settings for 5xxx or 6xxx series Radeons? I'm getting weird and low hashrates

Version of sgminer 4.1 which mines Vert successfully doesn't work on execoin

With 6870 I get 15-18Kh/s, thats absurd.
conf file is: (card has 1GB, hence lookup gap is 4)
"intensity" : "12",
"thread-concurrency" : "5600",
"worksize" : "256",
"lookup-gap" : "4",
"expiry" : "30",
"gpu-threads" : "2"
}