I am getting very poor gaming performance on my Windows 8 host OS with Hyper-V installed but no guest machines running.

For example World of Tanks reports 60-70 FPS without Hyper-V installed and 4-14 FPS with it installed. A similar, dramatic, hit is observed in several other games so the issue is not WoT specific.

To make the point clear, I am not trying to run games in a virtual machine. I don't even have a VM running while observing this effect. I simply have the Hyper-V feature installed.

My system specs:
AMD Phenom II 965 (3.4 GHz)
AMD Radeon 6950 2GB (XFX Double D HD-695X-CDFC)
16GB DDR3 1333
AMD 790GX chipset Mainboard (Gigabyte GA-MA790GPT-UD3H)

I have tried every AMD driver from 12.8 to the current 12.11beta8, virtualization is enabled in the BIOS settings, the onboard 3300HD video device is disabled in BIOS and I have read the MSDN blog entry here regarding a similar issue in Server 2008 that was resolved in 2008 R2 (and hopefully not regressed in Win 8).

I'd like to be able to use Hyper-V for development and testing at home (I am a sysadmin/software developer professionally). If, however, I can't also use my home system for entertainment I'll have to scrap those plans.