I saw RICHARD III when it was first released in 1955 and remember it very well. It certainly wasn't shown any wider than 1.66:1 or maybe 1.75:1. Incidentally, as far as I recall it was shown locally (outside central London) as a sort of roadshow presentation with separate performances but...
Here's an interesting article from Kinematograph Weekly, July 14, 1955, about the installation of VistaVision and demonstration of "Strategic air Command" at the Plaza, London.
http://i213.photobucket.com/albums/cc228/vanmunchen/img147.jpg
I notice that a number of M-G-M films credited Perspecta Sound in their main titles but which were also mixed in true stereo. I've never understood the logic behind that. Surely it would have been confusing when they showed the same film with those credits in theaters equiped to play magnetic...