GOP length for film?

[Dopopopolis]

The guides ive found that mention what the GOP settings for CCE SP 2.7 should be are either vague or conflicting. Take doom9's guide:

Change the N/M parameter to 4 for PAL content and leave it it at 5 for NTSC content.

but then this afterdawn guide says differently

A good rule of thumb is to plan for as close to 2 GOPs per second as you can get. If you're encoding video with a PAL framerate of 25fps you'll want to have a GOP with 1 I frame followed by a repeating pattern of 2 B frames and 1 P frame. The result would be a sequence of IBBPBBPBBPBB. To get this pattern you'd set the value for M to 3 indicating that every 3rd frame will be an I or P frame. Setting N to 4 will cause the pattern of an I or P frame and 2 B frames will cycle a maximum of 4 times in a GOP. Use the same settings for film sources (at 23.976fps) when encoding for NTSC, but for actual NTSC 29.97fps video you should use an N value of 5 to give you a half second GOP.

And CCE's manual says

Generally, M=3, N/M=5 is used for NTSC DVD, M=3, N/M=4 for PAL DVD.

When you create a stream for DVD with applying inverse 3:2 pulldown, M=3, N/M=4 should be set.



So what should be the N/M value for 23.97p film content?

[manono]

So what should be the N/M value for 23.97p film content?
Assuming you're also encoding for progressive 23.976fps, M=3, N/M=4. When Doom9 and the CCE manual suggest 5 for NTSC, they're referring to 29.97fps encodes. And you have to make allowances sometimes for the Japanese CCE manual writers not being very fluent in English.