I am kinda new at the whole GPU mining.  I am running Ubuntu 14.10 headless and the most I can squeeze out of my R9 280x is 68 MH/s.  I set gpu-miner -s 10 -c 1 which got me to 68, before I was at 65.  My card is fully stock.  Can someone please post what you have your core/memory set to.  I'll figure out the commands to set it.