I saw 2001 in 1968 when I was 8 years old, in 70mm. I remember that experience very clearly and LOVED the film, although obviously I don’t remember any details that would be useful here.
I also saw the film in 70mm at the Castro Theater early in its tour around the country in 2001 (before it got all beat up). That may have been the most astounding image I ever saw on the big screen. Corner to corner flawless, not even a piece of dust, with colors that leapt off the screen. The audience was sold out for each show, and loudly cheered at several points during the movie.