I did some research and according to IMDB
X-Men aspect ratio - 2.35 : 1
X2 X-Men United aspect ratio - 2.35 : 1 (Cinematographic Process Super 35)
X-Men The Last Stand aspect ratio - 2.35 : 1
Mars Attacks aspect ratio - 2.35 : 1
Austin Powers Goldmember aspect ratio - 2.35 : 1 (Cinematographic Process Super 35)Hope it helps from this information I would assume that the only ones that could be open matte would be X-Men 1 and Austin Powers
I think 300 might be partially opened, A Beautiful Mind might be open-matte, and I really would like to know about the X-Men trilogy.
You can see the 2.35:1 AR means anything opened up might be a plus.
Open-matte is a loose term and I prefer indicating if the frame is partially opened as opposed to fully opened. and I think S35 films are more likely to be partially opened.
I don’t have Spider-man screenshots, however, for collectors, the DVDs originally came with slipcovers. =)