Too young for the movie?

My 5-year old is obsessed with Godzilla, Mothra, Rodan, and Ultraman, and really wants me to take him to see Pacific Rim today. It is rated PG-13, but I'm assuming this is simply because of the violence between the kaiju and jaegers. He handles fictional violence like this well and has watched all of the recent Marvel movies (Captain America, all Iron Man pics, Hulk, Thor, Avengers) without a problem. That said, I will not show him any of the Dark Knight movies because I feel they are too dark and the violence is too realistic. For those who have seen it, any advice on taking him? Should I or should I not? Is the rating simply for fighting scenes or is there more I should be aware of (language, gore, etc.)? Any direction is helpful. Thanks!