I like Benedick. To the non-Shakespearean folks, it conjurs up feelings of betrayal, a la Benedict Arnold. To me, it conjurs up pictures of Kenneth Branagh looking cute.

For the time period in question, and his social background?

I think, alas, that it's either Bertram or Sebastian. Which is a pity, really, considering all the other names, but who he is and where he comes from has to be taken into account, as well.

Between those, Sebastian is better, imo.

I like Sebastian.

I like Sebastian best as a name, though I could see Demetrius working. Bertram, to me, has a nerdy feel.

I like Sebastian too.

My only concern with Sebastian is that it may be too much of a hero name--a little too much with the sexy and dashing and not enough with the pompous arse-ness.

Bertram, to me, has a nerdy feel.

It really does, doesn't it? But in the era and social structure in which Susan's story is set - early 19th century England - I don't think they'd invented nerds.

Of course, the character is something of a control freak. Sebastian might work. And I do like Demetrius, but how likely would this character's mama have been to use it?

Edit: x-post with the author! Susan, I also think that, with his personality, Titus would work. Very autocratic name.

Perhaps his given name is Sebastian but they call him by some other nickname? So that through most of the book, he doesn't seem very heroic?

He's not really the nickname type--part of his pomposity is that he's very serious and formal. But anyway, I'm now leaning toward using Sebastian and trusting my readers to figure out I've given him one of the standard Regency warrior-hero names ironically.