R9 280X 17.5 Mh
R9 270 non X 10.6 Mh
5870 7.3
No rejected, HW errors. Everything works fine
Can you tell me your 5870 setting please?

Sure
sgminer -k rockcoin -o stratum+tcp://www.rockcoinpool.com:3333 -u your -p your --thread-concurrency 8192 -I 18 --worksize 128 -g 2 --gpu-engine 900 --gpu-memclock 1200