I have set up 50 boards of Asrock H81 PRO BTC with the same exact cards as you are having, with Hynix Memory and they could not be overclocked through MSI Afterburner but only after downloading the bios mod.
What I can suggest you since you see THREAD STUCK IN DEVICE DRIVER, it is a driver problem and not a GPU or motherboard problem.
Here is what I did , completely uninstalled the existing driver with DDU(Display Driver Uninstaller,google it) it will do a thorough uninstall. Restart your PC and download the latest version from official website of ATI, keep the virtual memory both min and max 16384 MB (16GB) , install the drivers and I am sure you will have no more problems.
Since it worked on Asrock H81 PRO BTC should work also on B250 TB BTC as the motherboards are the same , have the exact same layout.
You can try Nicehash as a last resource.
I have also built several rigs with Asrock H81 Pro BTC mobos but I always used a different CPU since they use socket 1150. I want to believe this mobo is a great mobo for mining just as the H81 Pro BTC, and that is why I am also concerned about how harmful could it be for the mobo and gpu to run the system with the i3 3.9 ghz kaby lake CPU before updating the bios.
1151 Intel Core i3 Processor * 7100 QL38 3.9GHz 51W
*Please update system BIOS before upgrade your processor (CPU) to avoid system failure