From reading a comment by frogbeastegg I knew that the kneel ability was pretty devastating, but I haven't payed much attention to the calvary units. I mostly use saber cav, but now I'll have train some revolver cav.
I think that carbine calvary is an upgrade beyond revolver calvary - I imagine they pack a punch.

Ironclad - I knew it would be a powerful unit, but I didn't realize just how quickly it could rout/sink an enemy fleet.