Scott went to see Dunkirk in both 70mm IMAX and Dolby Cinema. He preferred 70mm though. Not a lot of deep blacks, but ultimately IMAX is best because that's how director Christopher Nolan shot it. And he shot it on the same beach in Dunkirk, Belgium with original aircraft and boats. The important point is that all the shots are framed within IMAX's square aspect ratio of 8x6. It makes it very immersive. Leo says it's a great movie, beautifully done. Scott agrees. And quite historic in its depiction.
Scott said, however, that the audio levels are painful, extremely loud at 105dB on the average. So if you go see it in IMAX, wear earplugs. There's not a lot of talking anyway.