I agree, strong typing is for weak minds. I work with a weak mind so I want strong typing.

There's no difference in speed between typing disciplines. In point of fact, there cannot be. You must know the structure of your data to program against it. Whether you write it down explicitly or implicitly changes nothing but the location you wrote it down.

My guess is that this is really a measure of how much abuse the language will tolerate. C# probably lets you get away with a bunch of things (like checking for nulls) that F# requires.