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.