Well, its true that the car still has radar, but that does not mean it is using it. I have not tried setting AP speed above 75, but following distance with AP on is not currently adjustable from the thumbwheel. I had AP on for most of the aforementioned 100 mile drive and it worked well--no weirdness, phontom braking, snuggling up to semis or anything (my frame of reference is AP 1 in my wife's X).
I kinda wish it would throw up a dialog on the screen say something "I am planning to brake for that stopped vehicle ahead, even though it might not seem like it right now"