Something that nobody ever seems to mention is that most studies on clutch have a lot of junk data in them that alters the results. What a typical study of clutch might do is take all of a hitter's plate appearances with RISP, and compare it to how they do without RISP. Or they'll take a player's performance in the postseason and compare it to their performance in the regular season. These approaches will include, in the "clutch plate appearance" category, a ton of situations that aren't actually clutch situations, and omit a lot of situations that are clutch situations. For example, if Ortiz is batting with runners in scoring position, but the Red Sox are winning by 4 runs, then it isn't a clutch situation, yet the study would hold it against Ortiz's clutchness when Ortiz pops out.
If Ortiz is batting in a tie game in the 8th or 9th or 15th inning with the bases empty and hits a home run, then that's quite clutch, but the study wouldn't count it towards Ortiz's clutchness because there were no men on base.
If Ortiz is batting with men on 2nd and 3rd with two outs and the Red Sox are down by 2, but the Red Sox are 10 games back in the standings and it's September, and Ortiz grounds out, then a clutch study would count this against his clutchness, even though it's not really a clutch at bat, because the Red Sox don't have much of a chance of making the playoffs, and therefore the situation isn't truly important.
If Ortiz hits a game-tying season-saving grand slam against Benoit in the ALCS, then a clutch study would treat this equally to another PA with RISP in the playoffs, even though a season-saving hit should count much more than another PA of less importance.
Getting a game-tying RBI when your team is 7 games up in the standings should not count as much towards clutchness as the same situation when your team is 1.0 GB in the standings, because there's much more tension and drama in the latter.
I think the best way to analyze a player's clutchness is to watch them play, and remember how they do in different mood situations. Also, weigh truly high stakes situations on their clutchness more than unimportant situations.