I've tried various parameter settings for this with no change, the only things I have not tried, is changing any of the GPU frequency settings, or upgraded the AMD drivers (still on 14.4). Although Pallas post shows stock should be able to hit around 18Mhs.
As for the .bin file, although I gave it a try, I did not expect it to make any difference, as that bin is for the Hawaii based GPUs, where as the 280x is a Tahiti card.
It should work on Tahiti as well (it works on 7950, so...)
I'm not sure what the issue is then, since new .bin files were being created even with your .bin in place, I decided to change the name of your Hawaii BIN file to match that of the file that was being created for my parameters, it does appear to use it, as no new .bin files are created, and only your one remains, but it also did not affect the hashrate either.
I also have a 7950 I can try it on later, to see how that fairs.