The Chicago Cubs, who boast baseball’s best record, have many strengths, but the key one is a lineup of such breadth and depth that you could slot any of six or seven regulars into the no. 3 spot in the batting order without anything seeming at all amiss. This is how you end up scoring half a run more per game than any other team in the league, as the Cubs have so far this year.

When you have that many strong hitters, some of them are going to end up at the bottom of the lineup, and Cubs games have presented all kinds of terrors to opposing pitchers looking for chances to coast. Second baseman Mark DeRosa, for instance, having batted no. 6 or no. 7 in 99 games this year, has a .481 slugging average and 77 runs batted in. Even more telling, rookie catcher Geovany Soto, who’s slugging .496 with 71 RBI while having started 77 games in one of those two lineup spots, often bats even lower in the crowded order. Monday, he batted no. 8, for the seventh time in the last month.

Soto may be better than what the Cubs generally get from that spot, but not by so much as you’d think. Collectively, the Cubs’ no. 8 hitters — center fielder Reed Johnson and shortstop Ronny Cedeno have started in the spot most, but players like DeRosa and right fielder Kosuke Fukudome have taken their turns, too — are hitting .290 BA/.353 OBA/.426 SLG this year. Cleanup man Aramis Ramirez told the Chicago Sun-Times earlier this week that the productive lower end of the order is “why we are where we are,” and if you can exaggerate the point — Chicago’s no. 8 hitters are just slightly better than Washington’s, and that team has a truly horrific offense — there’s still a bit to it. Pick a contender, and you’ll learn a lot about their offense by what they’re getting out of that lowly eight-hole.

Most of this year, for instance, the Mets have been jockeying with Philadelphia and Florida for first place in the National League East, and even now they’re essentially tied with the Phillies both in wins and runs. All three teams have structurally similar offenses, built around blinding young hitting talents like David Wright, Chase Utley, and Hanley Ramirez, and all three have a bit of a depth problem. Oddly enough, the three are getting more or less the same production out of their no. 8 hitters, with on-base plus slugging averages ranging from Florida’s .672 to the Mets’ .674 to Philadelphia’s .681, and rate fifth through seventh in OPS from the spot, which in each case is usually filled by an unexceptional catcher.

Out west, Arizona is one of four teams who have gotten at least a .700 OPS from their no. 8 hitters, despite having run through a cavalcade of utterly undistinguished catchers and second basemen in the spot. Fading Los Angeles, meanwhile, has barely been able to muster a .300 OBA out of lousy shortstops Angel Berroa and Chin-Lung Hu, replacements for the injured Rafael Furcal. This isn’t exactly a parable for how this race has gone, with Joe Torre’s push-button tactics leaving him getting less out of more than his rivals have, but it comes perilously close.

Most interesting, though, is what’s happening behind Chicago in the National League Central, where St. Louis manager Tony LaRussa and Milwaukee manager Ned Yost are running out lineups that rate, respectively, last and next-to-last in OPS from the no. 8 hitters, and for excellent reason. LaRussa has had his pitchers hitting there the entire year, using the nine-hole as a sort of second leadoff spot, while Yost did the same for the first two months and has had catcher Jason Kendall hitting eighth since.

It’s morbidly amusing that St. Louis’s eighth-placers (.195/.250/.294) aren’t doing all that much worse than Milwaukee’s (.217/.290/.271) despite the Brewers having the advantage of two months of Kendall, a purportedly real hitter. But what’s really telling is that the two teams are tussling for the wild card lead, and are scoring fewer runs than Chicago but as many as or more than anyone else. An ongoing experiment in finding out whether lightning strikes from on high if a team plays things slightly differently than proscribed by the famed Book has led to some results, and neither Miller Park nor Busch Stadium are in flames.

This, I think, is what there really is to learn here. The actual quality of the various teams’ no. 8 hitters is mildly interesting, but largely a function of how many good hitters they have. (If the Mets could bat Geovany Soto eighth rather than Brian Schneider, they doubtless would.) Where it isn’t — where the one team bats its pitchers eighth or lines the spot with men slugging near .500, or where the other team does what every team has done for all time and bats its mediocre catcher — we get a decent sense of which managers are running their clubs aggressively and which are doing what’s done because that’s what they’re supposed to do. That may not be a fair proxy for the sort of inventiveness that does a team well in October, but it’s at least something close to a tell.

tmarchman@nysun.com