Edit: Well, you learn something new every day. There was such a lens, but it was never turned into an AIS lens, and so the AI version was the end of it.
Here's what Bjorn Rorslett has to say about the 50/1.2 versus the 55/1.2
For the 50/1.2: "This lens replaced the older 55/1.2 and besides being neater and lighter, also offered a much better performance even at wide apertures. There is an endearing slight softness (bokeh) when the lens is deployed on a D1/D2-series camera and shot wide open, but the image even at f/1.2 has plenty of detail. Stopped down in the range f/2.8-f/5.6, image contrast is enhanced, sharpness is very good to excellent, and veiling flare has gone entirely. Quality deteriorates rapidly as expected with the lens stopped down beyond f/8."
And the 55/1.2: "This lens is impressive to behold, but image quality is modest when it is used wide open. There is a veiling flare from internal reflections that softens the image and coma is apparent at f/1.2. Residual optical aberrations lend a softness to the corners until the lens is stopped down to f/4-f/5.6, at which point it becomes a capable performer in terms of sharpness. Image contrast picks up beyond f/2.8 and is very good at f/8 to decline when the lens is stopped more down than this. Note that the 55/1.2 is susceptible to knocks from the side, such abuse can misalign the optical elements."
I occasionally use the 50/1.2, but have never shot with the 55/1.2. I think the general consensus is that the 50/1.2 is noticeably better than the 55/1.2 at the wider apertures.
It's fantastic, if you like the "classic" rendering style. Lots of spherical aberration, but very sharp stopped down. The 50/1.2 is harsher and more "modern" in its rendering.
Edit: Some old wide open shots with the Nikkor-S 55/1.2 pre-AI (same optics) on D700:
Makten, you have a shot for everything! Great job, btw
Most 55m 1.2 were non-AI and none were AI-S. Make sure it is either AI or AI-S converted if you plan on using on a digital body. I believe if memory serves right there was an S.C. version which had the best coatings of all.....I had that one a few years ago. Biggest complaint was being very prone to flare. Liked it very much and got me to purchasing a 50mm f/1.2 instead as everyone said it was even better. As Makten mentioned, the harsher bokeh wide open on the 50mm f/1.2 steered me away from that one pretty quickly.
My S-C is stellar, stopped down a bit, maybe 1.4 to 2.0. But as they say, @ 1.2 it's far better than a 1.8 lens @ 1.2...sometimes you just need massive light gathering ability. (and I still shoot about 90% film for low light work, unless somebody wants to donate a d700 or d3 to a needy returning to college after 30 years student)
Great job, btw