i see r9 280x can get more than 500khs, but i still cant get more than 320 khs per r9 280x. Already try Patched CG miner and Ultracoin miner, same problem. Whats i do wrong?

ultracoinminer --scrypt-jane --sj-nfmin 4 --sj-nfmax 30 --sj-time 1388361600 -o stratum+tcp://pickaxe.pool.pm:3306 -u xxxx -p x -I 13 -d 0 -d 1 -d 2 --gpu-threads 2 --worksize 256 --thread-concurrency 8193 -g 2 --gpu-memclock 1500,1500,1500 --gpu-engine 1090,1090,1070