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.