Fred, Fred, Fred. Shaking my head. Let me first say that the RBI stat has it's place. It is just not a very useful stat to assess a player without have some context to go with it. I think a very good example of that was the year that your favorite player Lugo had more RBIs than Pedroia.
More importantly, by the time players reach the MLB level, they are more or less all "clutch". In other words, the ones that are shaking in their cleats in pressure situations are either not going to make it to the majors or they are not going to last very long. A player cannot raise him game to an otherworldly level in a clutch situation. The good players simply maintain their composure and do what they normally do. Hitters who seem clutch are just typically good hitters.
Papi is not a great clutch hitter. He is a great hitter, period.