Gore to Plot Ratio / Fear Itself

Question: In a stock teen horror / slasher movie scenario (Scream, Darkness Falls, Harper's Island, Nightmare on Elm Street et al), what should the split be between horrific encounters/gruesome murder and investigation into the monster that leads to the final confrontation?

I'm thinking 30/70, with most of the screen time being tense, gory action.

I guess there's an argument for 10% of the movie being bare breasts and lustful activity and/or comedy, and about 5% being character development (oh, she's the Good Girl, he's the Brain, she's the Mean Girl, he's the Dumb Jock etc. Or, Alive, Dead, Dead, Dead, Dead, Dead).

I'm plotting out my first Fear Itself game, which uses the Gumshoe system, and I want to get the balance right.