1. Does this "as eloquent as well-chosen words are" mean "though well-chosen words are eloquent"?
2. "It(silence) is" is omitted before "eloquent", so is this kind of shortening by omitting suject+verb common and acceptable?
8)The opposite of talking is knowing when to stop. Speakers often have a problem with that. They're afraid that stopping might look like they forgot or lost what to say next. It's difficult to realize that as eloquent as well-chosen words are, silence is equally, and often more, eloquent. Eloquent not because it give the audience a chance to stop and think but because it compels them to do so...
2. Yes and yes. It's a matter of literary style.