Baseball reference has a "leverage" calculator for regular season situations:
If you want an actual example of a guy whose mid/high leverage stats trump his low leverage situation stats, well, David Ortiz:
Low 900 OPS
Mid 945 OPS
High 946 OPS
But what exactly does this prove? It proves that he's a guy who doesn't wilt under the spotlight, but you still can't present the argument that he's "clutch", because it's not a repeteable skill.
For the sake of argument, let's look at Bagwell, who you've made out to be "un-clutch" because of his failures in the postseason:
Low .938
Med .943
High .981
This is a guy who consistently played "up" to big moments and contribute to wins for the Astros, but all of it is dismissed because of the arbitrary idea of "clutch" assignment.