Sure, Chicago is undefeated, but what about the rest of the NFC? We’ll learn more when four of the conference’s one-loss teams play each other on Sunday.

PHILADELPHIA EAGLES (4-1) AT NEW ORLEANS SAINTS (4-1)
(Sunday, 1 p.m.)

Not only are both of these teams 4–1, but each loss came by a single score. Nonetheless, play-by-play breakdown shows that the Eagles have been the superior team this year in every phase of the game except for field goals and punt returns.

The biggest difference is on offense, where the Eagles are averaging 6.8 yards a play. That’s more than a full yard per play ahead of every other NFL team except the Giants (6.1). Donovan McNabb leads all quarterbacks in passing by nearly 300 yards. The Eagles still prefer the pass to the run, but when they do run, they’re the best team in the league, according to the Football Outsiders DVOA (Defense-adjusted Value Over Average) metrics.

DVOA ranks the Saints 10th in passing offense — better than anyone expected, but far below the Eagles.While veteran Joe Horn is getting his yardage as usual, the leading lights of the New Orleans passing game are both rookies. Nobody expected seventh-round pick Marques Colston from Hofstra to become the go-to guy for new Saints quarterback Drew Brees; he leads all rookies with 374 yards receiving. But everybody expected second overall pick Reggie Bush to get a lot of time as a slot receiver, and he’s second among all running backs in receiving yards.

Bush is quite similar to Eagles running back Brian Westbrook, and it will be fascinating to watch both players work against defenses designed to stop them. The Saints so far rank second in preventing gains on passes to running backs, the Eagles fourth.

Bush has been great as a receiver, but terrible as a runner. In college, USC could create huge holes for him, but with the Saints the holes are smaller, and Bush isn’t getting through them. Despite his legendary speed, linebackers have been getting to him on slowdeveloping outside runs before he is able to turn the corner and accelerate. As a result, he’s averaging barely three yards a carry — bad enough to cancel the benefits of a big comeback season from veteran Deuce McAllister. McAllister, averaging 4.8 yards, has a style far more suited to a Saints line that’s better at blocking up the middle.

McAllister should be able to gain yards against an Eagles run defense that’s been league-average so far. But DVOA ranks the Philadelphia pass defense fifth, while the New Orleans pass defense ranks just 15th.The Saints also must overcome an injury to rookie safety Roman Harper, replaced in the lineup by journeyman ex-Giant Omar Stoutmire.

Philadelphia is also dealing with injuries in the secondary, but starting cornerback Lito Sheppard played well in his return last week, and undrafted free agent Joselio Hanson actually managed to shut down superstar Terrell Owens for most of the game.

It all adds up to an easy Eagles win, except for one caveat, a variable that nobody can measure with numbers.The post-Katrina Saints have been energized by the crowd during their first two home games since returning to the Superdome, and that emotional lift could make this game much closer — or even produce an upset.

SEATTLE SEAHAWKS (4-1) AT ST. LOUIS RAMS (4-1)
(Sunday, 1 p.m.)

The Seahawks are underperforming expectations this year, while their archrivals in St. Louis are surpassing them. But it’s difficult to tell how good each of these teams is, because of the circumstances surrounding their wins and losses.

The Rams surprised the league by upsetting Denver on opening day, but since then have played four close games against four of the league’s worst teams — and actually lost to San Francisco. Opposing offenses have fumbled seven times and the lucky Rams have recovered all seven, a feat of total randomness rather than skill. Two of these fumbles weren’t even forced by the Rams defense, just quarterbacks dropping the snap, and one of those was Kurt Warner fumbling the ball away when Arizona was in field-goal range and down by just two points.

For 11 quarters of play to start the season, it looked like Seattle had fully defied the infamous Super Bowl Loser’s Curse. Then came the 27 garbage-time points they allowed the Giants in the fourth quarter of a game they once led 42–3, followed by a complete whitewash at the hands of the Chicago Bears. Despite a winning record, Seattle ranks just 19th in our DVOA ratings, solely because of these five quarters.

Seattle’s offense is plagued by injuries to running back Shaun Alexander and along the offensive line. Those problems are compounded by poor decision-making by usually steady quarterback Matt Hasselbeck. He threw only nine interceptions in 2005 but already has seven this year. The improved St. Louis pass defense, meanwhile, ranks second in the NFL with eight interceptions.

Seattle gets starting tight end Jerramy Stevens back from injury, but you may not see much of him on the field.The Rams lead the league in defense against tight ends, which is plenty of reason for the Seahawks to continue using the four-wideout set that’s become a staple since the trade for Deion Branch. While backup Maurice Morris has to fill in for Alexander, the Seahawks shouldn’t have trouble running the ball against a Rams defense giving up 4.7 yards a carry (24th in the NFL).

The Rams are back to being one of the league’s top offenses, despite a major change in philosophy with the hiring of head coach Scott Linehan. They run more and throw more short passes.But like every other Linehan team, the Rams stall out in the red zone, and kicker Jeff Wilkins leads the league in both field goals and attempts. The Seattle defense was dominant for the first 11 quarters of the season, and porous in the last five, so it’s not easy to gauge how good it really is.

Seattle looks like the better team, but like New Orleans, the Rams will enjoy a significant home-field advantage. The Seahawks have always had trouble winning at the Edward Jones Dome; even last year, when they were far better than the Rams, they beat them by just six points. While Seattle had the bye week off to prepare for this game, historical research shows that the team coming off the bye week has no advantage when both teams have winning records.

Mr. Schatz is the editor in chief of FootballOutsiders.com.