Let's consider the case of Bob Gibson as a clutch performer.
Gibson had 81 postseason innings to his credit. So, of course, the sample isn't large enough.
But those 81 innings came in a total of 9 games. That's right, an average of 9 innings per game. One 8-inning game, one 10-inning complete game, and 7 9-inning complete games.
The 9 games came in a total of 3 postseasons. They also came in a total of 3 series - the World Series of 1964, 1967 and 1968. This was before divisional play began.
So Gibson pitched 27 innings in each of 3 World Series. He pitched 5 games on 3 days rest and one game on 2 days rest.
For the 9 games he had a 1.89 ERA, a .89 WHIP and a 5.41 K/BB.
He was MVP of the 1964 and 1967 World Series.