Disabling Hardware Acceleration and Anti-Alaising see a notable decrease
in CPU usage; it still spikes but doesn't bring my system to a crawl.

Notably: This may be tied to the NVIDIA PowerMizer settings. So when
you're in "Adaptive" mode, it's supposed to spool up the clock speed on
the card when the power is needed. It looks to me like the "marching
ants" selection is taxing on the GPU, but PowerMizer often fails to
increase the card's clock speed when it's taxed by LibreOffice. What I'm
finding is:

+ If do something else that taxes the GPU, like initiate a transparent window 
somewhere, PowerMizer increases the clock speed, and LibreOffice begins 
performing better
+ If I set PowerMizer to "Maximum Performance" rather than adaptive, the 
problem goes away.
(however, Xorg still uses about 33% CPU whenever the marching ants are present)

I have not had a chance to try the nouveau drivers yet.

Do you think it's worth a continued investigation, or does this sound
like an NVIDIA bug?

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https://bugs.launchpad.net/bugs/1001550

Title:
  LibreOffice Calc causes high CPU usage in Xorg when displaying
  "marching ants"

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