The current AMD drivers in compute mode are optimized for Windows 10 v1709 FCU. Those are the fastest drivers to use with RX 570/580 cards. The only reason to use the blockchain drivers on Windows v1709 with RX 570/580's is some old miners like SGminer don't work with the latest drivers.
In my experience, in what mining is concerned, the Beta Blockchain drivers are identical to all new drivers. No speed difference whatsoever.
If someone has proof otherwise please come forward.
Beta blockchain drivers have a limit of upto 8 GPUs. New drivers don't... Speedwise maybe no difference so what is the harm of using newer drivers?