I agree with you about 8 sequence being the most natural. I'm too lazy to use it methodically, and 3 is easier to keep in my head without structure crowding out story, ,but the 8 sequence resolves a lot of problems of weak structure.

8 Sequence is an elaboration of the 1-2-2-3 partition (it's 1a 1b 2a 2b 2c 2d 3a 3b if I remember correctly). Even with 8 (or any other patterning) the mid-point is where a lot of unfilmed scripts fall apart--what's your take on that?