What is the config for 280X? I have this same configuration and any GPU mine at 7,27 Mh/s with sgminer of djm34. Thanks in advance. (Sorry for my english)
Update your drivers to 14.6 beta.
ANd be sure NOT to install goddamned AMD AHCI drivers

made my windows completely unbootable - even in safe mode :O
Had to reinstall, because the reason for the crash was identified after second "dead windows"... removing AHCI driver solved the problem...