I just popped on an old neonon (50, 2.8) I won on ebay at the same time as a new model schneider componon S and the Neonon is the better lens. On a 17 inch print from 35mm (f5.6, nicely aligned enlarger), the Neonon has better centre sharpness and corners and a MUCH nicer tonal scale. The mid tones are meatier (with a number of negs, off different films, and the prints just look a lot richer. It also has a touch higher contrast but Z5-7 are just much nicer to the eye even when the low and high values fall the same. Razor sharp.
Interesting as this eaxmple came in for about ten quid and turned out to have a tiny chip in the rear element. wont be letting this lens go....