I went to see the film today and really enjoyed it.
I went to see it at the IMAX in Cineworld, Birmingham.
Now I know that it's a digital IMAX cinema, but I went to see Oblivion at the same screen the movie filled the entire screen for all but one scene.
With iron man though there were black borders at the top and bottom of the screen throughout.
Both have the same aspect ratio listed.
imdb says the Imax version is 1.89:1 . Don't know if you get more or less in that version .
I think other films have done the same - Avatar in Imax was 1.85 , but 2.35 in the cinemas .
btw - what did you think of their Imax ? is it worth the extra ?