setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
cgminer --scrypt -o -u -p --thread-concurrency 8193 --lookup-gap 2 --gpu-engine 1027 --gpu-memclock 1500 --gpu-powertune 10 -w 256 -I 13 -g 2
This I have on my PowerColor R9 280x, I get around 710kH/s with it. 73c max gpu, 80~~ VRM1 @80% fan.
If it clocks down by itself you need to set --temp-target.
It's not always better to have high TC and high clock. Mine actually performs better at 950/1400 that at 1100/1700. A lot better.
You have to set the clock in your .bat file, start out with stock and you'll have around 700 on each card. Maybe more
Download HWInfo and watch your temps there, a lot of people forgets to look at VRM temp. If VRM temp is too high the GPU can throttle and underclock itself.
Oh yeah, and PowerColor is hotter than Sapphire if I remember correctly, so you should be below 70c with good airflow and the correct settings