Really curious situation,updated to 16.6.2 for having Rx 480 plugged in,installed driver all ok and then i noticed the hashrates:

Configuration: Win 10 64 bit
Video cards : 2x RX 480
1 x R9 390X Sapphire Nitro
1x R9 390X Gigabyte

Rx 480 mine at 27.8 with mem at 2200 the 390X Sapphire does 30.70 stock compared to 30.30 15.12 and the Gigabyte is 26 down from 30 on 15.12.

Why is Gigabyte R9 390X affected by the driver change and the R9 390X from Sapphire not?