Firstly, there are a lot more stats that indirectly measure speed than SB. For one, baseball-reference has a baserunning section on a player's "More Stats" tab. Secondly, I think we can get a crude measure of strong baserunning, or SPEED and I will attempt to do this by looking at two players who hit in front of similar lineups (in an attempt to control for that very important variable). Enter: Mike Trout and Austin Jackson. Both were leadoff hitters for lineups that were very strong 1-5 last year. Behind Jackson, hit Dirks/Santiago, Cabrera, Fielder, and Young. Behind Trout was Aybar, Pujols, Hunter, and Morales. More or less an equivalent 2-4, I think we can agree. Maybe even a slight edge to the Tigers. So, as a starting point, take RS%: the percentage of times a runner reaches base and scores. Trout had the edge, 44% to 40%. What might explain the difference then, if the hitters hitting behind Trout and Jackson were equally productive? Trout and Jackson made about the same number of outs on the bases (22 to 23), but Trout got on base 22 more times. So, they were picked off, thrown out, or caught stealing at almost the exact same rate. So its not baserunning blunders that separated them. Next we can try to solve for positive contributions. Jackson stole 12 bases in 292 opportunities. Trout stole 49 bases in 246 opportunities. Two other things we can look at are 1stS2 and 1stS3 - the number of times a runner reached 2nd and 3rd base (or home) respectively, when a single is hit. The Tigers hit 43 singles when Jackson was standing on 1st base. Of these, Jackson reached 2nd base 28 times, and reached 3rd base or scored, 15 times. But consider this: The Angels hit 45 singles hit when Trout was standing on 1st. Of these, Trout reached 2nd base 17 times. But 28 times he ran all the way to third or home. He actually took the extra base(s) more often than not. And that, I believe, accounts for that 4% variance in scoring efficiency. Over the course of 600 PAs, with a constant OBP of .399, that's 10 runs. A full win, separating a player with very good speed, and one with elite speed.