I can confirm that this worked on 1 of my RX570/RX580 machines.  I went into Device Manager, and updated the driver like the OP stated.  I only had to update 1 card, and it updated the rest for me.  My hashrate on a 7GPU system went from 184 to 192.  I am going to try it on an RX480 and RX470 machine, and will report back.