Couldn't agree with more with Lex, the Barshai 5th is truly great, you'll be hard pressed to find a more intense, fresh and spontaneous Mahler recording. Probably due to the fact that the orchestra consisted of young music students rather than seasoned professionals playing the piece for the umpteenth time, and the orchestra was also undoubtedly greatly inspired by its conductor. It's a shame we don'y have more recordings from this team. Makes you wonder who these kids were and where they are today, in particular the lead brass players who yield nothing to their big-name counterparts in the top orchestras.
What's even more fascinating about the Barshai recording is that unlike most "live recordings" that are in fact patched together from several concerts and rehelsars, it is an unedited one-off recording of a single concert, nothing added, nothing removed.