Good point about matching the casing to the opening. I have several different size openings - regular size doors, small double hungs, medium double hungs, wide double hungs (actually two double hungs next to each other), and a cased opening that's about 6 feet wide.

You think I should find something wider for the cased opening? There is a door and some windows in close proximity to the cased opening. Might it look odd to have different size casing on that opening than on the adjacent doors and windows?

EDIT: Following up on my83300cd's comment, the cased opening is the same height as the adjacent door, so I will probably trim them the same. Make sense?