I had three sticks this past year, all intermediates, one 60 flex, one 70, one 75 (though it felt stiffer).
With the 75, I barely felt it flex. The 70 was hit or miss like you describe. The 60 felt like it was whipping a ton with every shot.
We're all different of course, but I experienced the same thing - I went with a 67 flex in a Bauer x4.0 and it is, as Goldilocks says, "just right". To be fair I have to cut it down an inch, so its likely closer to 69-70 flex.