Right this moment the config that gives me less rejected shares (around 20%) is:
del *.bin
sgminer -k darkcoin -o stratum+tcp://XXX -p XXX -I 19 -w 256 -g 1 --lookup-gap 2 --thread-concurrency 8192,8192,8192,8192 --gpu-memclock 1500,1500,1500,1500 --gpu-engine 1175,1175,1175,1175
GPUs are R9280X from Asus
Thank you
Mine configuration (-d 0 is 280X, -d 1 is 270)
color 0F
sgminer -k darkcoin -d 0,1 -o stratum+tcp://pool -u user -p pass --thread-concurrency 11200,21568 -I 13,19 --gpu-engine 1100,1200 --gpu-memclock 1500,1500 -w 256 -g 2,1 --no-submit-stale --lookup-gap 2 --failover-only -o stratum+tcp://poolBackup -u user -p pass