Yes your link is right. For me, my 280x give me the following Hash : - QUBIT : 5.5 Mh/s - MYR-GROESTL : 19.4 Mh/s
I don't use skein, it seems to be more stressfull for my graphical card.
My Msi 280x give 27mh/s for 1100/1200 stable.
28 MHs? Wow, i have a 280x trixx, at 1100 stable, 60°C. It's 9 Mhs more than mine. Can you maybe give me the link of your modified sph-sgminer? I have probably not the latest kernels.