Last September, Shane Black did an interview with Jim Vejvoda at IGN, and the subject of "Doc Savage" came up. Black was discussing the casting challenge that Doc Savage poses, since the character was always described as being larger than anyone else, exponentially speaking. You could do it as an effect, I'm sure, but it helps if you start with someone who's already gigantic.
To that end, Jim suggested Chris Hemsworth. I concur. During a recent event of some sort that I might be heavily embargoed over, I may or may not have had reason to see Hemsworth in person in a very particular costume that showed off just how absurdly proportioned he is. I'm a long-time Doc Savage fan, and I know how I've pictured the character based on the way character in the stories react to him. He is unsettlingly large. He doesn't quite seem to be the same species as the normal human men around him. I think Hemsworth totally works if you're trying to cast that, and it helps that he is crazy talented as well. I think it would be fun to watch him play a lead in a Shane Black film, since I'm sure Black's take will have plenty of sly character humor built in, and Hemsworth is great at playing things so straight that they become funny.