I read an article recently which considered this question of metal vs stocks, the author  splitting the market into 2 time zones. This article was about gold. Splitting the market into 2001-2005and 2006-2012 ..  In 2001-2005 stocks (HUI) outperformed the metal (gold) by a wide margin (7x), while 2006-2012 it was the other way around! Then he considers 2001-2012 'the entirety of the gold market", and HUI wins at 1.7x. So at this time, according to him, stocks are undervalued relative to the metal..

http://www.kitco.com/ind/Hamlin/20121113.html