After tweaking an AMD r9 280x with 14.9 Drivers on x11 Algorithm I got a stable 4.3Mhs with these settings on sph-sgminer_x13mod.
--kernel x11mod -o stratum+tcp://ilt.suprnova.cc:5510 -u Username -p password --thread-concurrency 8192 -I 19 --lookup-gap 2 -w 256 -g 2 --gpu-engine 1175 --gpu-memclock 1500
14.9 sucks , you have to take 14.7RC3
14.7 RC3 is givin all HW errors in sph-sgminer_x11mod sgminer 4.1.0 ! And nothing else! Just tested!