For the R9 series, 15.12 remains the "go-to" driver version - nothing later is more efficient, a LOT of the later drivers give worse results.
I honestly don't think AMD bothers testing the "Relive" series on the R9 cards, since they want you to move to the RX series and Vega instead of sticking with 3+ year old card designs.
I run the latest 17.6.2 drivers and don't really see much difference going back to 15.12. I'm running 390X's.
when i run the 15.12 on Groestl i get about 41 MHS if i run anything else its 21 and i have a 390