The Valkyrie was one of those high tech wonders that bankrupted the Soviet Union. It was capable of Mac 3+ and in 1966 would have dashed by all Soviet Air Defense systems. The high powered radars and long range missiles would be countered by the foloowon F-111B and the Soviets, thanks to Reagan and the resurrected B-1, would be outspent and outdone.
Crossfield had the "Right Stuff" and it's too bad he didn't get a shot at Apollo! It took Rutan to beat his X-15 records with SpaceShipOne!!!