I am selling this one because I also have the black one.
In the past, Zeiss lenses do not have contrast as good as Leica at f2. This Planar outperforms other Contax lenses at f2, it is similar to Summicron 50 2 at f2 in terms of contrast and resolution.
This Planar 50 2 and Summicron 50 2 are very much the same at most f nos. This Planar is slightly sharper at f4 and higher. On the other hand, Summicron has better contrast, I mean large object contrast characterized by the line 5lp/mm in the MTF graph.
The colour reproduction of the Planar is more frank,whereas Summicron has the traditional colour rendition of Leica. The tone turns slightly more cyan.
In terms of Bokeh, this Planar is definitely better than Summicron. It has no signs of astigmatism except at the very margin of the photo.
If you like better colours, go for Zeiss. If you like better contrast, go for Leica.