You know there are killer performances by somebody that you'd love to see released from the vaults. My candidate: the 18 hours of total riffs that Robin Williams did for his DJ character in Good Morning, Vietnam. Mere minutes got used but there's so much more hidden away that would just leave you gasping for air. http://www.imdb.com/title/tt0093105/?ref_=fn_al_tt_1 << It's so damn sad that his demons finally consumed him.
Got some candidates?