Thought I would share some of my own recent (and highly insane) tests!
I was getting weird spikes on a brand new Xeon workstation build. My older 2008 computer ran 7.5 fine. I noticed that it was centered primarily around locating the cursor in the project - clicking here, clicking there. After further experimentation, I realized it was caused by doing anything mouse-heavy. So, I did the following:
--Disabled my high-end Radeon GPU.
--Reverted to the on-board Intel integrated graphics.
--UNINSTALLED the Intel graphics driver, and used the generic Microsoft (!) driver (weird, but keep reading...)
--I went to the Troubleshooting tab of the graphics adapter, clicked the "Change Settings..." button, and moved the "Hardware Acceleration" slider one notch to the left (read about trying this in an old Nuendo forum post). For further info see http://www.wikihow.com/Turn-off-Hardware-Acceleration. I only moved it ONE notch, not all the way off!
Guess what: all CPU spike problems completely disappeared .
For confirmation, I then updated the generic driver to use the latest Intel build, and all the problems reappeared . In my case it is definitely related to the graphics rendering -- and what's weird is that using generic (software) rendering is an improvement!
The problem is that you can't just move this slider and forget about it, because the Change Settings... --> Hardware Acceleration slider is only available when using the generic Microsoft driver -- the entire "Change Settings" button is greyed out when using any vendor-specific drivers :(
FWIW, moving the slider one notch to the left disables "cursor and bitmap accelerations."
Try it yourself and see if the same thing happens for you! If so, this is definitely worth pursuing from a Support perspective.