there are at least a couple very low hanging fruits for us developers to enjoy, thanks wolf0 for helping preserve the specie ;-)
Tsss! Don't tell anyone about prepatched kernels!

I'm in the 600 Mh/s club: 621 on r9 290x@1100.
Now wolf0 will reply "I'm at 700+"... ;-)
My current results.

R9 290 @ 1000MHz: 547MH/s
R9 280x @ 1150MHz: 504MH/s
R9 270 @ 1123MHz: 309MH/s
7990 @ 1000MHz: 438MH/s (per GPU)
Just to brag a bit more, I actually had these already before Wolf's latest release.

I think the Hawaii would easily be 600+ with decent clocks..