New version of AMD miner was added to OP, this new miner gives higher hashrate. If you have previously used old version of the miner then you should add 6 to your intensity, e.g. -I 13 corresponds to -I 19 in new miner.
I've compiled AMD miner for linux and I'm getting segfault when I try to launch it.
Try version from girino, I believe he is using it on linux so it should work:
https://github.com/girino/spreadcoinx11-sgminerI don't have linux machine with a GPU but I will try to test it anyway, at least it should launch.