Have you tested by installing driver manually?
File name: win64_154010.4300.zip
Please follow steps same as Windows® 8.1 for manual installation: Desktop graphics drivers — How to Manually Install a Driver in Microsoft Windows 8* or Windows 8.1*
Manual installation from zip file worked, using the device manager. So I could install the latest beta driver 22.214.171.12426.
Excellent, I am glad to hear that manual installation has worked for your computer.