I had the exact same problems as Makyl and DummyO. I was running 12.8 drivers on Windows 8 with no problems folding.
I updated to 12.11 Beta4 and was stuck at 35% GPU usage. Uninstalled beta drivers, installed 12.10, and I was still stuck at 35%. Next, I completely removed my 6870, ran driver sweeper, and then re-installed 12.8. After all that I was still stuck at 35% usage.
I was about to re-install Windows 8 when I remembered that, with no SSD in my folding rig, I still had System Restore on. I restored to a time before I installed 12.11, and I was back up and running.
Originally Posted by DummyO
An almost identical situation happened to me. Thus how I stumbled upon this post. I have a Win 8 box with HD7970 that seemed to be running 100% until I got back from a business trip this week. Now it sits at ~35%. I also upgraded to the 12.11 beta drivers and suspected it, but am now on the 12.8 (the 12.10 won't install for me anymore) and still see the same problem. I was reading the foldingforum and the only conclusion that I can come to is that these new AMD units are not as GPU intensive as they used to be and something else is the bottleneck.
See this link for more details to my suspicions: http://foldingforum.org/viewtopic.php?p=211806#p211806
The WU's for AMD are still the same, and those posts are referring to Nvidia WU's which are not the same as AMD WU's.
There is definitely a driver issue with 12.11 and folding. I haven't tried to install 12.10 since I got back up and running on 12.8, so I am not sure if the problem exists in 12.10.
Long story short, since I don't game on my 6870, and the 12.11 beta is only an upgrade for the 7xxx series GPUs I would suggest sticking to 12.8. Depending on the games you play 12.11 may not be a big performance increase for your 7850.