Howard had several plays yesterday that would have resulted in negative plays for Langford simply because he's got way more power than Langford does and is able to muscle through some of those arm tackles. That being said, in games where the Oline can open up holes like they did against Indy, Langford will shine with his speed. That 58 yarder would have been a house call for Langford.
I think they will complement each other well, but Howard already appears to be the better grinder who gets those tough yards after contact. That's something we've been missing for a while and it's really nice to see.