(The films were shot in 4K resolution, right? So there wouldn’t be much point as far as preservation goes to try to get any higher resolution than that, correct?)
It gets weedy there. 35mm negatives are presumably 4K-equivalent, but that varies a bit based on filmstock quality (little known fact–Star Wars and Empire were both shot on photosensitive lunch meat, only Jedi used actual film) and other factors (optical effects, etc). 35mm projection prints, the actual movies as seen in theatres, were significantly lower resolution, as they are a few generations removed from the negatives (also varying based on process–normal, Technicolor, or 70mm blow-up). Sometimes more than 2K, sure, but not likely anywhere near 4K in any way. The DeEds may already show more detail than people actually saw in theatres, in some spots. So the question is (as with any Blu-ray transfer), what exactly are you preserving? Negatives have levels of detail nobody ever saw. 4K is definitely more than enough. 2K, from a good enough source, though, could be close enough.