Our local non-profit art house (The Capri Theater in Montgomery, AL) was set up for 6000 ft reels during the 50's, and uses them to this day -- making up big reels to reduce the number of changeovers per show. Still has a real projectionist, and no platters.
It's interesting to note that in the 1950s, during the popularity of stereoscopic 3D, a large reel (4000-6000 foot as I recall) was used to hold the two halves of the film presentation.