Its not really the length of the movie that determines result - allthough it can be a guideline that this might be a difficult movie.
Its the size of the original movievobs, the average bitrate of the original movie, the quality of the original movie and how difficult/complex the content of the original movie is.
Result is determined by how much the transcodingengine has to lower the bitrate to make the vobs small enough to fit on a 4.7 gb dvd-r.
Quality of the original movie is also very important as the transcodingengine use the same encodingscheme as the original, only lowers the bitrate. Most of the titles you mention are older movies and quality of those are bound to be less than some of the new movies.