Monroe - I get a cool artsy vibe from this without it seeming too hipster.
Montgomery - I immediately think of [name_u]Montgomery[/name_u] [name_m]Clift[/name_m] and the kind of men he played, i.e. serious and sensitive. I agree that [name_m]Monty[/name_m] is a cute nickname that definitely lightens the name and brings a different charm to it.
Lawrence - This seems like a very adult name to me. I like the [name_u]Laurie[/name_u] nickname option though which I think makes it less dated.
Berkely - I think this is a serious but down to earth name.
Sullivan - The more I consider this name, the more I like it. It seems very friendly and gives off an intelligent vibe.
Whitman - I just think of [name_m]Walt[/name_m] [name_m]Whitman[/name_m], so it seems like a surname to me. I think it would be a lot for a child to carry, but with the right nickname it could work.