Showscan was 65mm shot, 70 mm projected at 60fps. I worked on a Showscan production in Australia in the late 1980s. An unblimped camera running 65mm film @ 60fps sounded like the loudest dentist drill. The camera op had to wear industrial earmuffs. I was recording sound (wild) of a bagpipe band two city blocks away just to not hear the infernal machine ramp up to shoot speed. Insane but astounding images.
Trumbull’s research was that above 50fps was the sweet spot and 60 being 2.5 x 24fps was the logical rate. I found it interesting that 48fps was chosen for The Hobbit which made sense for a 3D image, although I remember the howls of disgust when traditionalists thought it looked like ‘video’. I think higher frame rates are a good idea with 3D. In fact Trumbull went on to develop a 3D 4k system at 120fps called Magi.