Cessna has a hypersonic version of their C 162 but it's also classified...
Seriously do you know how much heat is generated at the tip of the wings at Mach 5? Don't forget that the melting point of Titanium is 3135°F (1725°C) and that at the difference to the Balckbird (and derived) the X-15 can fly in rarefied air environment (it's rocket propelled).
BTW never heard about your declination of the SR-71. I knew about the A-11, A-12, M-21, YF-12 and SR-71A-B-C.
This is what I found concerning the D-2
