Turn off the Aero Glass theme of Windows 7!
When I select the Aero Basic theme, most (not all) clicks and pops disappear. Please try and tell, if this works for you as well…
Out of curiosity, what’s the WDDM version of your graphic card and on how many screens do you run your system?
I done a little experiment while mixing yesterday:
If You turn off all windows except edit (which will turn off the document) - edit window I minimised
The CPU usage DROPS by 30% !!!
In other words, if Cubase don’t have to show those gradients, buttons and other eye candy, the Cubase works fine
Except… then You don’t see what you doing 
Did you try to disable Aero Glass then?
I assume that Steinbergs pretentious graphics framework is the culprit. For comparison, Reapers graphics engine on the same system has no bad impact on audio performance, even when Aero Glass is active.
But this assumption needs more user tests and feedbacks.
Running background services with priority does it for me (as well as disabling enhancements to the UI).