I wouldn’t distinguish between either of them. It’s pretty clear that performance in Late-Inning Pressure Situations (LIPS, no kidding, ah those wacky stat-heads) is wildly variable from year to year. There are VERY few (and I mean less than 10 and possibly zero) who consistently performance better in LIPS than at other times. The fact is that a good hitter is a good hitter. The ‘clutch’ label that is applied to some usually gets that way through a few highly-publicized instances.
Kind of like Joe Carter was considered a great hitter because he consistently produced 100 RBI and ended a World Series with a home run. Well and good but look overall and he’s overrated.
Plus, RBI itself is HIGHLY context-dependent. Different players get different opportunities to produce RBIs depending on the players in front of them. Put Babe Ruth in a lineup with 8 Mark Lemke’s and Ruth’s RBI will be weak. Put Mark Lemke in a lineup with 8 Babes and you’ll see Lemke produce 100 each year.
RBI and ‘clutch’ are just too context dependent and prone to variation to indicate much.
I utterly guarantee you that this information is available. The full results of each at bat are tracked, pitch-by-pitch and within context (score, runners in what positions, temperature, etc), for every major league game. With enough digging this stat could be produced.