I'm going for "YES".
As I said earlier, Downey is a fantastic actor. He's got serious gravitas and will bring credibility to this role for the mainstream audience. So I have no fears regarding his acting ability; he's got chops.
But I guess I am slightly concerned with his physical aesthetics. Stark is a handsome, rich playboy that every woman wants a piece of. Not saying that Robert isn't a good-looking guy, but he isn't that
kind of good-looking. But I will say however, that with a stache and goatee Robert does have a striking resemblance to the character.
Overall I am very confident with the choice, with just a slight reservation.