I don't want to sound rude, but here is some friendly advice.
I don't know how can you compare mindfuckery on a one dimensional scale. (alright - there is something to it. Clearly one movie might be meant to screw someone's mind, while the other only mildly puts our heads to spin, but I'm still appalled at the try) The point is - you might actually be thinking about how hard a movie is to understand instead of... well... whatever definition of mindfuck you want to take.
And if you really must use a scale, describe it.
"1" could be "1st class mindfuck", making 5 a lot worse (less fuck-inflicting
) experience. Of course from the list I could make out you are going the other way around it. (1-5 being an increasing amount of mindfuck)
This applies to any made up scale.
To the list alone -
Cashback?! Even 1 would be too much for me (yay using the scale badly already). I mean - it's a good movie. Very good considering it was a début for significant part of its makers, but it didn't put on my braincells much work, let alone any form of intellectual intercourse.
Moon? 3-4 (again if the scale goes towards more mindbending experience) This film is not much of a mindfuck as it is a twist. And the reveal isn't that much of an impact either - for a Sci-fi story it isn't. Not if you've read enough good sci-fi books.
Try the novel: "The Metamorphosis of Prime Intellect" - I can guarantee you it will widen your scale for sci-fi genre alone quite a bit. (free online, but heed my trigger warnings traveller, for it features violence and very
Apocalypse now - sorry, but "Jacob's Ladder" holds the mindfuck title over all others in this genre for me.
Again - just a commentary. I didn't mean to discourage you from anything. You might have just hit a few of my pet peeves in rapid succession and I had to blow some steam off in the general direction of your part of the Internets.
PS - I don't think I've ever written "fuck" so many times in a post. Not even when I used it as a comma I didn't.