Military grade

I can neither confirm or deny the SR-71 max speed or max altitude. To summarize, mil spec wire or cables has nothing to do with sound quality.

There are specific MIL STANDARDS for many things for many different reasons. You would have to read the particular standard for whatever cables you have in mind. Undoubtedly some cables are specified to be able to withstand temperature extremes, salt, water, shock, etc. but other cables might not be specified that way, but some other way. Depends on application. Also undoubtedly, military specifications for cables would not (rpt not) address sound quality per se, in audiophile terms.

I take it the cryo was just window dressing.