I have almost the exact same system and had a similar problem. In 6.02 the Hyper threading was not working right with the CUDA. Read this link for a solution that got my Z820 back into the Supersonic speed mode. Look for EC Bownes posts.
https://forums.adobe.com/thread/1061522?tstart=120
Heres a selection of that thread…
63. ECBowen,
Sep 7, 2012 5:15 PM in reply to ComputerNovice25
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I think I have an idea what is going on now. It seems the new update has significantly optimized the Cuda block allocation going on in the background. When I was testing at 16GB of ram I saw far more fluctuation of ram usage going as low as 4GB on the same project that normally pushes 10 to 13GB with all threads active. When all threads are active the ram usage is staying relatively consistent at 8 to 11GB with far less flushing. However with far more ram available it seems the optimizations are triggering some Windows 7 ACPI Power management features that are shutting down cores as not needed even though the actual application really could use the processing to complete the task. Each system board has different ACPI sets that will adjust what Windows 7 does, how, and when regarding power management. This would explain why this is not consistent. This unfortunately is looking like a side effect of optimizations to the Cuda Player Memory allocation and not a bug. Lasvideo you may have to make those registry adjustments after all since this may not be fixable on Adobe’s side.
Eric
ADK
At the thread Eric provides a solution to the problem that nails it.
Tom Daigon
PrP / After Effects Editor
http://www.hdshotsandcuts.com
https://www.youtube.com/watch?v=XRIg6h-LIm0 (Best viewed at 1080P and full screen)
HP Z820 Dual 2687
64GB ram
Dulce DQg2 16TB raid