I tried on a clean install of 32-bit ubuntu with latest (may23) 14.6 beta drivers, but I do not get any speed increase at all. I tried on x11mod both with djm34's version from github and latest sgminer v5.0.
A friend sent me pre-built .bin files from Windows and that works, I get 3.8 MH/s instead of 2.9 MH/s on my ASUS R9 280X. But if I build them myself on my Ubuntu, I get no speed increase (just normal 2.9 MH/s).
Any idea what I'm doing wrong? Does it have to be 64-bit?