I have tried now the latest SGMiner from this link: https://www.dropbox.com/s/59lvecndm866bzz/sph-sgminer_x11mod_b2.zip and getting following results:

280x -> 3,33Mh/s
290 -> 3,73 Mh/s

Config (280x,280x,290):
sgminer --kernel x11mod -o stratum+tcp://useast.blackcoinpool.com:3333 -u UserName.1 -p x -I 15,15,15 -w 128,128,256 --thread-concurrency 8192,8192,25601 --gpu-memclock 1500,1500,1250 --gpu-engine 1090,1090,1000 --gpu-fan 60 --gpu-powertune 20 -g 2,2,4

The pool is showing hashrate accordingly but I'm seeing this error popping up frequently:

getaddrinfo() in setup_stratum_socket() returned 11001: No such host is known

What is this error?