The difference between Fitzgerald's intelligence and Orwell's doublethink, as I see it, is that Orwell's doublethink is when the conflicting ideas are understood as binary absolutes, held to exactly represent reality, while Fitzgerald's intelligence is when the conflicting ideas are understood as fuzzy approximations held to convey something important about the world without exactly representing it.

And, going further, I think the root of the danger found in Orwell's doublethink lies even lower -- the danger starts with holding even one idea as a binary absolute that perfectly reflects the real world. Ideas, particularly ideas which can be reduced to language, are more like Platonic forms, which elements of the natural world might fuzzily reflect but will never perfectly embody.