When the question usually is, "How fast will it go?", what is the answer to, "How slow will it go?"
Here's the story. Involving a WWII British airfield, a flyby with cloud cover and a low ceiling, and an SR-71 sideways at 152 knots in full afterburner.
UPDATE 7 February 2018 21:22 [Borepatch]: This is a very cool story. I posted one a long time back, if you're a SR-71 fan.