[V_Terranova_Jr]

> I do wonder how much modern design can overcome, in materials, engines, aerodynamics, and flight controls.

The basic physics are arrayed against you. Higher speed cruise flight already means you already fly at higher altitudes or the thermal and structural loads would be intolerable. Stall departure resistance isn't the issue. Get high enough, and you're no longer talking about cruising flight, you're talking about hypersonic glide that has been accelerated to hypervelocity by rockets (this is called point-to-point boost-glide). It has been looked at, and people are continuing to look at it. There is a whole loose industry coalition in the U.S. called "FastForward" that is interested in this topic.