Baseball Prospectus readers may be familiar with this already, but here's an article at ESPN about clutch hitters. It's an excerpt from the BP book. It discusses Tony Perez but doesn't draw any conclusions about him. It does name the best clutch hitter since 1972, however.
One other thing. It says a lead-off out is more than twice as costly as the last out of an inning. I think I know what they're getting at, but I'd think the last out of an inning would be infinitely costly.