Last night I was watching the latest computer graphics extravaganza to come out of Hollywood. The easy answer to your question is that there is no maximum resolution in pixels for photographic film.
Pixels are a computer thing.
The smaller the dots, the more you can pack in per square inch and the greater the detail they can convey. Film doesn't work this way. A film image is created not by dots but by blobs of colored dye with continuous gradations of tone. When projecting film, a light is shone through the film and the blobs of color show up on the screen. No pixels involved.