I have two powercolor 280x's.  Here's my stable x11 config.  The lower gpu engine one is Elpida and the higher a Hynix card.


c:\sgminer.exe --kernel darkcoin --auto-fan -I 19,19 --thread-concurrency 11200,11200 -w 256,256 -g 1,1 --temp-target 70,70 --temp-overheat 80,80 --temp-cutoff 90,90 --gpu-powertune 20,20 --gpu-engine 1010,1090 --gpu-memclock 1500,1500

Hope it helps some....