I also have a Asus Strix RX 580. My hashrate is about 27,5 now (claymore dual mining)
I tried the Uber-mix settings (extreme and the less extreme) but both crash my PC.
I only copied 1750 strap to the 2000 strap and overclock memory with 50 mhz. More makes it instable (reboots etc).
Would love to get a bit higher has rate. Weird that Uber-mix settings don't work at all.