I've got a couple of questions regarding jackets. If I'm posting this in the wrong place, please forgive a newbie.

First, is there a hard and fast rule at all regarding which one is more formal than the other? They have very similar silhouettes, and I'm at a loss as to which one is "classier" than the other.

Second, would it be a serious faux pas to wear either one with slacks? I want to expand my wardrobe, and need another sport coat anyway, and figure if I can get away with a "two birds with one stone" solution, it would help convince the love of my life that it's not a completely frivolous purchase...