Experimental data. I posted an extensive list of parameters for this setup on the previous page. I wish overclocking GPU RAM increased hashrate too, but it didn't.
I was really hoping I could get 280h/s out of my 380X's using the settings you shared for your 280x, however, they lower my hash rate to about 209h/s per card. For me, setting my GPU clock to 900mhz and my RAM clock to 1625mhz produces the best result on the 380x in terms of performance/efficiency at 220h/s. Sure I can overclock my GPU to bring them up to 228h/s if I increase the ram to 1640mhz and uses an 1100mhz gpu clock as you suggested, but it uses so much more power I'm worse off. Just increasing the GPU to 1100 from 900 does nothing for me. I truly think this maybe a card dependent question.
@Claymore, my offer still stands, how much ZEC will it take to get you to make some improvements for the R9 380X (Tonga) in your next release?
I run both of those cards on one system using the 15.12 drivers and am getting 289 H/s on the 280x, and 217 H/s on the 380. It doesn't appear that the power management functions are working on the command line either. I might try the new drivers to see, but it could be a hassle for nothing.