Though I usually use deluxe, I've seen De Luxe used, especially in referring to items on a dinner menu (I.E. Crab Imperial De Luxe). Hmmm...now I'm wondering if there's a precedent for beverage size...whether it's usually deluxe or De Luxe, as in small, medium, large, de...? Dr. Bill's example does handily clarify the distinction between the two.

(Howdy Kintucky! Good to see your smiling name again, Jackie!)