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Javier: I think what you are seeing in terms of b&w is a difference in character--that is, a difference in the grain structure of the film. This is the easiest thing to identify when comparing prints. As you have observed, traditional b&w (such as Tri-X) has a distinctive and more pronounced grain, and 400CN has a sharper, less grainy look. Also, the rendering of the grays will vary between the two films.

I, too, sometimes have difficulty noticing the differences between a consumer grade color film (i.e. Superia 200 or 400) and the "pro" color films, such as Pro 160C. I do not do enlargements, as they are expensive. I opt for quality 4"x6" matte prints--plain and simple. They are also great for photo albums, and, while some may consider the 4"x6" format small, I would note that not too long ago (in the 1960s and 1970s), the common print size was 3.5"x3.5" (3"x3", not including borders). I still have a 3.5"x3.5" photo of me (taken by my mother in 1970). At the time, I was a child. That little shot conveys quite a message. The 4"x6" print size is also full frame for 35mm. Those 8x10s that people seem to like so much are, in 35mm, missing 20% of the shot (full frame would be 8"x12").

Regards,
Glen