That discrepancy between the Bernstein Shostakovich Fifth and the score tempo markings has always struck me. Particularly after coming across a 1981 film by Aleksandr Sokurov called "Sonata for Viola" - a Shostakovich biopic from the Soviet Union. It includes a taped telephone conversation between Shostakovich and the great David Oistrakh. At one point Oistrakh plays a portion of the Sonata into the phone. The composer gives his approval - to which Oistrakh comments that his playing isn't even close to the metronome marking in the score. Shostakovich reaffirms his approval, then wryly comments, "what do I know, I'm only the composer."
It seems Dmitri Shostakovich was a man who allowed artists a great deal of latitude, and was not terribly hung up on exactitude - so long as the interpreter got to the heart of his idea. Mravinsky's interpretation and the original concept may have a darker menace, but I can see how the manic quality of Lenny's interpretation would appeal to a composer felt hemmed in by critics and detractors on every side.
As usual, a great and provocative week of programming. Continue the good work.