BK,
Your PSYCHO references brought back memories. I recall seeing the film for the first time at the Paramount Theater in Seattle. During several scenes, my date dug her fingernails into my arm.
I used PSYCHO as an example of three-act structure in my writing class last weekend. Interestingly, one could remove all of Janet Leigh's scenes from the picture; begin it with Vera Miles' search for her sister...and you would still have a viable picture.
Yes, you would have to add a few scenes to the 2nd and 3rd acts, but it would still work, because the basic plot is the search to find Janet Leigh and the stolen money. Janet's scenes are, essentially, prologue to this.
Don't misunderstand. I am not suggesting that anybody tamper with this classic. But, from a strictly structural standpoint, that's how the story breaks down.