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.