It took a week longer than promised but AMD finally has a new Catalyst beta driver, you can download Catalyst 15.5 Beta over here. This release is the recommended driver for The Witcher 3 and Project Cars.
Highlights of AMD Catalyst 15.5 Beta Windows Driver:
Crossfire Profile Update for:
The Witcher 3 - Wild Hunt
Performance Improvements for the following :
The Witcher 3 - Wild Hunt : Up to 10% performance increase on single GPU Radeon R9 and R7 Series graphics products
Project Cars - Up to 17% performance increase on single GPU Radeon R9 and R7 Series graphics products
For further information on how to optimize your drivers for The Witcher 3 - Wild Hunt and AMD CrossFire™ please read the following article.
??The Witcher 3 - Wild Hunt : To enable the best performance and experience in Crossfire, users must disable Anti-Aliasing from the games video-post processing options. Some random flickering may occur when using Crossfire. If the issue is affecting the game experience, as a work around we suggest disabling Crossfire while we continue to work with CD Projekt Red to resolve this issue
 Project CARS: Corruption may be observed if Anti-Aliasing is set to DS2M when run in Crossfire mode. As a workaround we suggest using a different Anti-Aliasing method.