The SR-71's top speed is still classified to this day, partly because they probably still don't know what it was, because nobody ever got one there. Shul's plane was cruising probably far below max speed (the number wasn't 1942, I don't remember exactly what he said it was).

As to "not using the same freq", military aircraft have radios with knobs that turn. They can certainly monitor and talk on civilian frequencies if they see fit to do so, and they fly in and out of civilian airports regularly on ferry flights (not the SR-71 obviously, but I know for a fact F-18s do all the time, because I used to stand duty at a command that owned a bunch of them and we had to file reports on what airport they were at). If they can't talk on civilian frequencies, how would that work? And they fly through civilian ATC owned airspace, they absolutely have to talk to civilian ATC.

As to Shul being removed from the program, have never heard that -- I'm not likely to take the word of some random on the internet about it.