Comparing performance with Windows running in Parallels is not a valid comparison. The OpenGL driver in Parallels is inadequate for Rhino, and Rhino turns off a lot of its advanced OpenGL drawing features when it sees a deficient OpenGL driver.
If you want to compare with Rhino for Windows, you would need to boot into Windows and run Rhino there for a valid comparison.
If you still see a significant difference, please
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Post your Rhino for Mac info from About Rhinoceros > More Info…
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Post a screen shot of your OpenGL settings from Windows Rhino.
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Post the model you are using for your tests.