What type of rod is it--iron, wood? How are you hanging the curtains--on a rod pocket, rings, clips? What type of heading is on the panels? What style of room is it? For a window that wide, you will need several supports.

Please post some photos.

I'm using black iron rods, there's no pleating in the heading and I'll be using clip-rings. The room is pretty much transitional with a hint of modern farmhouse.

A picture would be nice, but you say its a large opening so I would say the larger of the two would be appropriate.

I agree, smileythecat, the 1 1/8" would be better.