@ Bajawah

You could try the following:

{
"pools" : [

]
,
"rawintensity" : "8192",
"vectors" : "1",
"worksize" : "256",
"kernel" : "scrypt",
"lookup-gap" : "2",
"thread-concurrency" : "9728",
"shaders" : "2048",
"gpu-engine" : "1000",
"gpu-fan" : "60-85",
"gpu-memclock" : "1500",
"gpu-memdiff" : "0",
"gpu-powertune" : "0",
"gpu-vddc" : "0.000",
"temp-cutoff" : "85",
"temp-overheat" : "80",
"temp-target" : "70",
-other stuff-

On the 280x Gigabyte this gives me 340-350 kHash, no Hardware errors.

EDIT

I see you have set your memclock to 1800. try setting it to 1500 as i think the 280's are not really stable above that point.

As far as I can see the Kevminer is more stable then the official one. As to your question what value's I am using (I've got an Asus 7950):

rawintensity: 1048576
threadconc: 19712
gpu-engine: 1000
gpu-memcl: 1500

gives me a nice 290+ khash, without any hardware errors whatsoever.
Hope I could be of help.