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.
I have a six card RX 570/580 rig with dual boot Windows 10 v1709 partitions. The latest Adrenaline drivers on one and the Aug 23rd blockchain drivers on the other, so I can run older miners that are not compatible with the current drivers if I need to. Using the same settings for both, in addition to the blockchain drivers being noticeably slower by 3-4 MH/s, they have frequent drops in hash rate and issues with Windows as well. The AMD blockchain drivers came out before the Windows 10 v1709 FCU and are NOT supported. The v1709 FCU was a major update to how Windows interacts with GPU's and also expanding the previous GPU limit from 8 to 13, which is why AMD had to release new drivers that were compatible with the FCU.
In what 1709 is concerned, might be, but I run 1703 and on it there a re no differences between drivers.
Also you loose AB rpm graph settings if you update to 1709 and new drivers (and I'm not referring to the graphical interface but to the graph definition of it as a mathematical function).
Also I have only max of 7 cards, so 8 limit doesn't bother me.