Although there has been plenty of speculation, I find it very difficult to believe the Yanks have a Mach 5 Spyplane... When you do the math for the skin temperarature (Stagnation at the nose cone and leading edges), its well above the melting point of Titanium.And well into weakening many modern metals including Nimonics and steel. Not that they could be used, simply far too heavy. Plus, the bl**dy thing would be visable for miles, the IR signal would be enormous, similar to that of an incoming Ballistic missile. Although it would not really matter, flying far faster and higher than any (current) Air defence system, other than Directed Energy. Ben Rich, designer of the SR-71 air inlets and Director of Skunk Works when it built the F-117 stated that Regan's dreams of a Mach 5 Spy plane were unreallistic, as the limits of the materials they were using were at their limits. And thats with using the fuel as a heat sink.
Besides, who needs a mach 5 spyplane when you have plenty of Synthetic apature radar UAV's and such like? Plus all the satilites you could dream of?