This is good to see. AMD has released Radeon Software Crimson Edition 16.5.1 to align with Forza Motorsport 6: Apex. The drivers are classified as Beta, and so is the game, coincidentally, which means 16.5.1 is not WHQL-certified. That doesn't have the weight that it used to, though. Its only listed feature is performance improvements with that title, especially for the R9 Fury X graphics card. Game-specific optimizations near launch appear to be getting consistent, and that was an area that AMD really needed to improve upon, historically.
There are a handful of known issues, but they don't seem particularly concerning. The AMD Gaming Evolved overlay may crash in some titles, and The Witcher 3 may flicker in Crossfire, both of which could be annoying if they affect a game that you have been focusing on, but that's about it. There might be other issues (and improvements) that are not listed in the notes, but that's all I have to work on at the moment.
If you're interested in Forza 6: Apex, check out AMD's download page.