... Who goes around making medium gray test prints on grade 5 paper? I suppose some nerd somewhere will think it's great fun.
John Sexton promotes this in his workshop as a technique to check the evenness of lens and light source illumination. I second his approach, because it works well as a test. That makes two nerds. There may be more!
How are you using them? If you are not doing big enlargements, you are only using the center anyway. For big enlargements, the corner resolution will fall off to some extent with all 3. Easly minimized by a longer focal length lens or a "High Magnification" lens of the same focal length.
How do you figure that if you don't crop? OK, it's true if you do crop, but I don't always do that. They're all good to about 11x or maybe a little more. That's often much more than I need and I never need more for a 35mm negative. I mean, 11x enlargement is an 11x16 inch print from that size negative and honestly, even that's too much most of the time. It's the rare negative that's even good enough for a print that big. The enlarging lens is the last thing you need to worry about.
As you move the enlarging lens closer to the negative (focusing for a big enlargement) the image circle gets smaller.
Large format taking lens manufacturers frequently give the image circle at infinity. The image circle is twice as big at 1:1.
Since enlarging lenses are never used at infinity, a stated image circle at that focal point is a little useless. Process lenses sometimes are listed with image circles at 1:1. In general enlarging lens image circles are not stated by the manufacture probably because neither 1:1 or infinity are common uses of enlarging lenses. But, just be because they don't state the image circle, doesn't mean an enlarging lens has infinite coverage or or doesn't follow the laws of physics
Hmmm .... you guys are talking tech. stuff... I have this lens (63mm), a Rodenstock Apo-fancy something & a Focatar 2. The specs are better on the Roden. & terrible on the Leitz, but the Leitz is my go-to 90% of the time because it is simple beautiful. Nikkor 2nd ... APO ... well it's sharp anyway.