AMD has just posted some Catalyst 15.5 beta drivers in response to the releases of Project Cars and The Witcher 3.
The official release notes are pretty sparse, but they mention a CrossFire profile update for The Witcher 3. They also anticipate performance gains of up to 10% for R9 and R7-series single GPUs with the beta driver. Performance is likewise improved in Project Cars, but this time up to a quoted maximum of 17% (again, in single-GPU mode).
The Witcher 3 gets even more special attention. AMD offers a handy optimization guide addressing most of the performance issues revealed upon the game's release. However, the release notes recommend that users disable post-process anti-aliasing with CrossFire. There may still be some random flickering occurring, with the only workaround for the latter being to disable Crossfire completely.
CrossFire issues rear their head again in Project Cars, with a note about graphical corruption with DS2M anti-aliasing enabled. That issue looks fairly minor in the grand scheme of things, though.
Get'em while they're hot, folks.