Updating complex parts of a widget instead of all of the widget many times a second takes a lot of CPU on Mac OS X

This use case is to update a widget containing close to 100 meters where the meters update many times a second.
To optimize the performance, only the part of the widget that is changed is updated. When this is done, the application uses from 50 - 100% CPU on Mac.
The same code on Win uses close to 0% CPU.

When updating the entire widget every time the CPU load is considerably lower.
This contradicts the performance gain you should have by not updating everything all the time.