James at 2010-02-04 19:23:46:
I don't see any of them as mutually exclusive.
For example -- 3 Act vs 4 Act is really an arbitrary decision on how big of an impact your Midpoint is.
In ALIENS, at the midpoint the marines are ambushed by a horde of aliens. This forces them to change their tactic from advancing and extermination to retreat and survive.
However their objective is STILL to destroy the aliens. So --
Did the midpoint constitute an Act Break?
Does it matter?
The structure is still in place regardless of what you call it.