I have the exact same problem with the beta 13.6 driver with GPU Tweak as well as Sapphire Trixx and MSI Afterburner with voltage control enabled.
I have AMD cards and the funny thing is the windows 8.1 driver that i should be using with 8.1 does it on it's own without the software, bit random, anyone else or is it just me?.
I know they have added new dx11 features to 8.1 but wouldn't feature levels stop any major compatibility issues. The extra features may or may not be available to different software/hardware but isn't it all just dx11_x, or whatever. I get that is a preview but shouldn't these included features imply that it'll be taken up by the gaming community quickly.
Kinda seems like I've had a software upgrade for a better UI and a couple of extra features and everything else is broke. :mad:
Windows and drivers are not gpu tweaks fault of course, though saying that my cards are ASUS, and did come with a shiny 'windows 8 compatible' sticker.