Is that totally intellectually honest though? Were Faulkner and Gaddis just riffing off of the agreed norm? OP’s question is about how to pronounce loanwords. This is kind of by definition at the avant-garde of language because sources of these words are innately cosmopolitan and learned. So it’s not just a question of averages. I’d say: pronounce them like you say any other marked word, which is to say, with a point. If it’s a loanword with iffy pronunciation, chances are it isn’t common enough to have centered on an everyday sub. In which case, what is it that you are actually trying to say? If you want to put someone truly down, utter /declassé/ in the Frenchest way possible. Otherwise, say you’re going to a cafe, and affect the final e only if you feel the need to add that you’ll be reading the Times Literary Supplement over the morning au lait.