Do you need to win five tricks or six?

Edgar Fiedler, an economist who worked under presidents Nixon and Ford, said, "Ask five economists and you'll get five different answers - six if one went to Harvard."

In this deal, how would you play the club suit if you need five tricks? What if you require six?

South is in six no-trump and West leads the heart jack. With the given hands, what should he do? And suppose the diamond king were only the queen. How would that affect declarer's approach?