In a previous life, around 1980 I suppose, I was flying out of Changi one night, seat 56J as usual. I got talking to the chap next to me who turned out to have flown the SR-71. There's no doubt he wasn't Walter Mitty - I knew just enough about the aircraft to accept he knew what he was talking about.
He said the weirdest thing about the aircraft was that, as you went though M?, the fuel flows just wound right down to next to nothing. We spent the next few hours trying to figure this out. I'll let you know when I've got it.