"largest area" immediately brought "A Sunday Afternoon on the Island of La Grande Jatte" to mind - not for actual impact, just because the physical painting is nearly 10 feet across, which noone seems to expect. Also it's on one wall of an enormous room with plenty of room for people to circulate, in a gallery that has various options for free access (mostly aimed at locals and students, but the art institute doesn't seem too picky about it.)