I have the 50mm PE and consider it an excellent all-around wide angle. If I only had one wide lens for my ETRSi that would be it. I've also had both the MC and PE versions of the 40mm lens and never noticed any differences in optical quality. The PE lenses, however, have a more elegant design and user-friendly aperture ring. I always found the aperture ring on the 40mm MC awkward to use. But the main reason I have all PE lenses is age. The newest MC lenses are around 25 years old and the oldest ones are 36 years old.