, it would better define the problem if you could fill in the blank:
CPU usage with nVidia's driver and non-nVidia glx: 95%
CPU usage with nVidia's driver and nVidia's glx: ___________
Your cooperation could open up new avenues of diagnosis.
For example, if you fill the blank with "95%", that would mean it doesn't matter what glx you use - it would rule out your use of non-nVidia glx as the cause. We could then move on to other possible causes.
If you fill the blank with "<5%", that would mean nVidia's driver has difficult to reproduce bugs when interacting with non-nVidia glx - maybe they only show up with a hardened kernel or with certain graphics card models.
This is why we have been asking you to try it just once with nVidia's glx.