Seems like I remember reading a blog where there were some gamer-programmers who had these huge log files to process. Using C# it was just too much -- it took too long. But by using F# (and block operations I think?) they reduced it to some crazy time like 5 minutes or something.

Theoretically they should be the same; they all run on the CLR. But I think F# lends itself to stuff like tail-recursion and data operations such that the code has a tendency to self-optimize as you write it, which is kinda neat.