I've used old versions of both f/4 and f/2.8 El-Nikkors. The F/4 version is better than many of the other brand f/3.5 or f/4 three or four element lenses, but the f/2.8 version is better yet. Wide open it provides quick and precise focusing. Stopped down to f/4 it performs well from corner to corner. It might be at its best at f/5.6. When stopped down below f/8, the effects of diffraction become visible on the sharpness of grain. The effect in the center of the image when stopping down can conveniently be seen with a strong focusing aid. Some focusing aids permit this even at the corners of the image.

Decades ago I did a quick, but critical, test of about 35 camera and enlarging lenses. Four were better than any others: an El-Nikkor 50mm f/2.8, a Micro-Nikkor 55mm f/3.5, a Leitz Elmar 50mm f/2.8, and a GN-Nikkor 45mm f/2.8. Other 50mm lenses from Nikon and Leica lagged slightly behind those four. The Nikkor 20mm f/3.5 of 1967 was one of the sharpest in the center of the field, but much less so near the edges.