If this helps anyone, here's the config file I use to get 6.8 MHS out of 3 280x GPUs:
.\sgminer -k darkcoin -o stratum+tcp://stratum.multipoolmining.com:5555 -u my wallet address -p x --lookup-gap 2 --thread-concurrency 8192 -g 2 -I 13 --auto-fan --gpu-fan 0-85 --temp-cutoff 90 --temp-overheat 85 --temp-target 70 --gpu-memclock 1500 --gpu-engine 1180 --gpu-powertune +1
I played with many configs to come up with this one.
I get the similar hash rate with 4 x 280x. But mine are Gigabyte and are notorious for hahsing less than other brands. I get 1.6 average each.
dude, check these settings
https://docs.zoho.com/sheet/published.do?rid=12cbm2fe8ce55abb2476daa0f8c576b442d40&mode=htmland maybe you should check your drivers too before making any changes.
i run a single gigabyte r9 290 at ~2.4 mh/s but i have it underclocked and undervolted and it pulls 120watts off the wall, i find it the best ratio for now