In the very near future AMD will be releasing an updated driver, focused on improving performance in Prey and DiRT 4. 

For DiRT 4 it will enable a Multi GPU profile and up to 30% performance improvement when using 8xMSAA on a Radeon RX 580 8GB compared to the previous release.

Prey is not quite so impressive, but you can expect a 4% boost on the same card.   Drop by the driver page to grab them, or keep an eye out in your Catalyst Control Panel.