[Katsunami]

When adding weight, I'd expect that the margins around the letters will get smaller. That will give you less room for setting a small line spacing. With the normal Caecilia, setting the smallest spacing is no problem. I don't find it too dense. (I find more spacing to be too loose.)

If I'd be using a fatter Caecillia, it may be different of course.

Even though it's thinner than Caecilia, I like Palatino. The size is too big though: on theb same size settings, I lose 4 lines of text per screen, compared to Caecilia. Baskerville is okayish (problems with c and e, for me), but it's too small. It gains 4 lines per screen compared to Caecilia. Setting Baskerville one setting bigger, or Palatino one setting smaller, makes them just a tad too big or small for me.

Caecillia is just right in weight and size; the only thing it has against it is that it is not a beautiful font. It doesn't have the grace that Palatino and Baskerville have.