sgminer.exe -k darkcoin -o stratum+tcp://stratum1.suchpool.pw:3339 -u x.1 -p x -I 11 -g 2 -w 256 --lookup-gap 2 --thread-concurrency 8192
I found that most rigs need the setx parameters with X11 despite lower thread concurrency (for scrypt you only need it with high thread concurrency)
This wil give me still hardware errors with a speed of about 1Mh/s per gpu card.
The other setting:
sgminer.exe -k darkcoin -o stratum+tcp://stratum1.suchpool.pw:3339 -u HrqxJyeguRvFcGU.1 -p x -I 13 -g 2 -w 400 --lookup-gap 2 --thread-concurrency 8192
also give hardware errors but much much more speed. about 2.2 Mh/s per gpu.
Don't know what i have to change

also don't know what speed is acceptable at the moment.
it seems odd that you get pretty much spot on the mhs but with errors (would usually be much lower or much higher). Do you mind posting a screenshot of sgminer running?
Also, did you add the setx parameters?
Also add --gpu-engine 1040 --gpu-memclock 1400