For B&W film, Summaron tones I like more, as if more gradations from black to white. C-Biogon's contrast is striking, similar to Summicron 35 Asph. Both have almost no distortion, bokeh by the Biogon is buttery smooth. Center sharpness of Summaron and the C-Biogon is almost the same, f2.8 and f5.6 tested; a tiny tad to Summaron's favor. The C-Biogon is superior in the edges/corners. For color and digital the C-Biogon is an outstanding lens.
Not to undermine; Summaron's center sharpness was better than any 35mm lens I have tested including the Summicron Asph and Summicron v1.