You didn't much discuss order. I think, unless the younger film is a clearly superior film, the default ought be release date. The older film should play first.

Idon't know that I would consider sequels to be the makings of a good double bill. The one film being contingent upon the other for its very existence abrogates the sense of equality the phrase 'double bill'' suggests...

But I take your point about length. In theory, a double bill with 'The Searchers' and 'Jeremiah Johnson' sounds life-altering but in practice, probably not so much... or, perhaps, rather, too much.

The question becomes what happens when you put two films together? Does your experience of the films change? Do you change?

For another Western pairing, I think I'd put Anthony Mann's 'Winchester '73' on the bill with 'Silverado' for their respective sprawls and light touches. Yeah, 'Silverado' is a little sappy, but 'Winchester '73' is more than a little racist. I think putting these two together blunts the edges of their flaws which might allow you to see more in each film.

For a Christmas pairing: I think I'd show ' Scrooged', followed by 'Elf,' as they are both good movies that re-weave some of the Christmas tropes lightly, and playfully around themselves.. You might even be able to slip in the trailer to Elf at the beginning of 'Scrooged', between 'Robert Goulet's Cajun Christmas' and 'The Night The Reindeer Died' for an... ahem... easter-egg, of sorts.

For war movies I'd put Kubriks 'Paths of Glory' and 'Saving Private Ryan' together... you know... purely in the interest of recreational melancholy. I think there is a certain intensity to Kirk Douglas' character in 'Paths' that is matched by by both Tom Hanks and Matt Damon in 'Saving Private Ryan.'