KEF - FLL and return on an Icelandair 757
Also MAN - MCO on a charter 757 many years ago, although that had a touchdown in Bangor, Maine, where we deplaned, cleared customs and immigration and had a chance to stretch our legs. IIRC the return was nonstop.
BTW, the Immigration officer at Bangor was the friendliest immigration officer I've ever encountered anywhere in the World...