I'm going to stick my neck out and comment without reference to tests. I have used a Leitz 40/2.8, 50/4.5 and El Nikkor 50/2.8. The 40/2.8 was the sharpest under the loupe. A clean late Leitz 50/4.5 and El Nikkor are similar. I have Leitz 50/4.5s which have lower contrast than the El Nikkor. Condition of the lens make a large difference. The older Leitz optics tend to not be as clean as a late model El Nikkor.