Okay, over at Joy of Sox are Ortiz's stats in walk-off situations (i.e., plate appearances in which if he hits a HR, game over, the Sox win). Read the whole post, but quickly, since the end of the 2004 regular season:
BA: 11-for-14 (0.786)
OBP: 16-for-19 (0.842)
SLG: 32 bases (2.286)
His OPS in those situations is over 3. Uh...wow.