I found an interesting scientific paper on the resolution of 35mm film going from the negative to watching a release print on a movie screen. If I understand correctly, the average discernible resolution by experts of a 35mm film viewed in the theatre is about 720p, but I could be mistaken, so I think poita can probably shed more light on the process used by these people:
https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7262540