According to lensrentals.com the GM is is in the same class as the new Nikon and Canon EF 24-70mm lenses.
https://www.lensrentals.com/blog/20...s-the-24-70mm-f2-8-gm-mtf-and-variance-tests/
https://www.lensrentals.com/blog/20...s-the-24-70mm-f2-8-gm-mtf-and-variance-tests/