The 75mm is indeed a great lens. However, from my experience, 95% of the time, I am almost certain that there is little discernible image quality difference between it and the Sigma 60mm f/2.8, especially for the type of shots that you have shown, i.e. from f/2.8 to f/4. There may be 5% of the time, most probably much less, when I actually need that extra speed faster than f/2.8 or want to use it at that aperture due to the hassle in focusing and in fact inadequate DOF for most tight head shots. I can understand however how fondly most owners talk about the lens, due to its build, its AF, and extra bokeh or emotional reasons. For most portrait shooting with reasonable lighting, honestly, I have to say that the difference between the Sigma and the 75mm in actual use and in results is negligible. The IQ difference is more noticeable when comparing one of these lenses with the 45mm f/1.8.
