My number one pick would be Once Upon A Time In The West on Alchemy - I love the studio recording but was amazed when I first heard the live version with the long but highly melodic guitar solo which never comes close to getting boring or self-indulgent. The studio Once Upon A Time doesn't begin to hint at the second half of the Alchemy version, which reaches Dark Side/Wish You Were Here-era Pink Floyd levels of transcendent beauty in my opinion.