Silas is one of my absolute favorite names (too bad the husband doesn't like it!). I also think it's the one on your list that goes best with Atticus.
I'm not a huge fan of either Ezra or Inigo--I just can't see them on a child, but that's a personal opinion. Lucius reminds me too much of Lucius Malfoy from Harry Potter. I actually also like Caspian, but it would be my second choice. My vote's for Silas!
Ezra- Awesome name, and quite distinct from Atticus... but it does feel a bit Biblical next to Atticus...
Silas- A bit too similar to Atticus for me...
Lucius (Loo-Shus)- too similar to Atticus
Inigo- My name is Inigo Montoya... Prepare to die. I only like this as a mn,
Caspian- Love. It is distinctive from Atticus, but ties them together with them both being quite literary names. I wanted to use this name, but DH is Iranian, and felt it would be like naming our son Tehran or something... I've never met a young Caspian, but would love to do so...
Caspian is my favorite as well! :)
My vote goes to Caspian!