I seem to be mining this okay with my R9 270X's..... Here is my bat file for anyone interested... Seem to be getting around the following on each card: 1.225M/976Kh/s.

setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
C:\CRYPTO\SPH-SGMiner\sgminer.exe -k darkcoin -o stratum+tcp://hiro.suprnova.cc:3313 -u xxxxxx.xxxxxx-p xxxxxxx --thread-concurrency 14208,14208,14208 -I 20,20,20-g 1 -w 256 --gpu-fan 85 --lookup-gap 2 --gpu-engine 1050,1050,1050 --gpu-memclock 1400,1400,1400 --gpu-powertune 20 --no-submit-stale