I’ve said this over and over: depending on the condition of the print, 70mm showings can look great but only if the film was shot in large format (65mm, VistaVision, Todd AO, Super Panavision 70, Ultra Panavision 70, Camera 65, Dimension 150).
35mm upgraded to 70mm (i.e., The Wild Bunch) is fine as far as it goes but nothing to necessarily shout and scream about.
The bottom line today is that digital projection tends to look just as good as 70mm, and in some cases better (i.e., no print degradation). 70mm can look great, yes, but it’s mostly a marketing brand that film cognoscenti have bought into — a way to “sell” classic movies.
In and of themselves, 70mm showings are no longer the coin of the realm.
