This driver is legit.
I run 6x RX480 Sapphire Nitro+OC 8GB cards. I get about an 8 Mh/s increase with it, from under 160 Mh/s to 168 Mh/s, dual mining with Claymore ETH and Siacoin.
I run a custom bios on all of them that has the 1750 timing straps copied to the 2000 and set the CPU downclocked to 1125Mhz.
I use a monitor emulator dongle and WattTool to drop the voltage -16 (100mv) and currently run the cards at 2070 Mhz.
I was previously only able to get 2050 Mhz before stability issues occured (daily hangs or reboots.)
Total power consumption as monitored by HWinfo/Corsair AX1200i is about 1000 Watts, so no increase in power draw.
HWInfo GPU memory errors are minimal and within acceptable range.
Wattool not working with these drivers, and probably won't work anymore even with official AMD drivers, if they leave the ADL as it is now on this beta.
Wattool is not updated anymore, a long time ago.