I bought a 45P with my FM3a over 10 years ago when they were still new. I never warmed to the 45P. I was hoping the bokeh would be smooth and nicely rounded, I found it to be rather clinical, not terrible but not what I was looking for. The lens is small, too small for me - I don't have large hands or need gloves in the NZ climate, but it was fiddly to operate - when turning the narrow aperture ring I would often touch the focus ring by mistake. Lack of solid real-estate on the barrel made it harder to grip when putting on and off the camera. The f/2.8 aperture also felt too slow for a standard lens. Maybe that's an odd thing to say, I used the 55/2.8 micro for years without complaining about the speed, and I rarely shoot at wider apertures, but I still felt I wanted more speed in a non-macro standard lens. I eventually sold it and switched to the AI 50/1.8 - this lens has much better ergonomics, is over a stop faster and the rendition, while not perfect is smooth enough for me. That was back in the days of film, I never used the 45P on a digital camera.
As for the 45GN, the later "C" multicoated version should give contrast and color fidelity nearly as good as the newer 45P. With only 6 glass-air surfaces the contrast should be high in any case, especially if the front lens is shaded from strong light.
