Greg Biffle is off to his best start since 2005, when he won two of the first seven Cup races, but it's not enough.

Biffle is the only driver with top-10 finishes in each of the first six Sprint Cup races and is second in points, just 14 behind Jimmie Johnson.

But it's not enough.

Not nearly enough to challenge Johnson and stop him from winning a fifth straight Sprint Cup title.

And Biffle knows it.

"We've been good so far, and that's not good enough," Biffle says.

Not nearly good enough. Not when Johnson has won three of the first six races, already has the points lead and is off to the best start of his career.

"A person's going to have to be great; you'll have to be flawless at this (to beat Johnson)," Biffle says. "We've been good everywhere we've been. That's not good enough. We're going to have to be better than that."

So will everyone else.

The first six races of the season have established whom Johnson will have to worry about most in his quest for a fifth title.

Biffle, Matt Kenseth, Kevin Harvick, Jeff Burton and Kurt Busch have all gotten off to good starts. Jeff Gordon and Tony Stewart aren't far behind.

Mark Martin, Kyle Busch and Denny Hamlin, meanwhile, have some work to do to get back into Chase contention.

The key question after six races is, can anyone beat Johnson, the overwhelming championship favorite again this season?

And will NASCAR's new spoiler, which will be used for the second time this season Saturday at Phoenix International Raceway, level the playing field and close the gap between Johnson's No. 48 Hendrick team and everyone else?

And how long will it take Johnson and his top challengers to adjust to the new spoiler?

The next three races on the Sprint Cup circuit will help answer those questions, providing three distinctly different challenges.

Phoenix is a flat, one-mile oval that races as much like a short track as a speedway. It's also a track where Johnson and Hendrick Motorsports have dominated in recent years.

Hendrick drivers have won the past six races at Phoenix, with Johnson taking four of the past five.

If the spoiler is the great equalizer, it should begin to show at Phoenix.

After Phoenix, the circuit heads to 1.5-mile Texas Motor Speedway, a fast track that will present the best test yet for the new spoiler.

Texas has produced 15 different winners in its 18-race history, with only Burton and Carl Edwards winning multiple times.

Johnson has just one win there and Hendrick teams have won just three times at Texas. Biffle, Kenseth, Edwards and Roush Fenway Racing, meanwhile, have excelled at Texas, with Roush drivers winning there seven times.

With aerodynamics and downforce at a premium, the drivers and teams that adjust to the new spoiler quickest will find themselves at the front at Texas.

Following Texas is Talladega, where the entire Cup field tested with the new spoiler a few weeks ago. The spoiler and a larger restrictor plate are expected to lead to higher speeds and a faster closing rate in the draft, making that race as dicey and dangerous as ever.

Like always, Talladega will be a crapshoot, where everyone has a chance to win and anyone's season can take a downward turn in a hurry.

Following Texas is Richmond, another short track, and Darlington, a high-banked, downforce track where the spoiler will also be critical.

The top five drivers in points after nine races last year -- Kurt Busch, Gordon, Johnson, Stewart and Hamlin -- all made the Chase and wound up being serious championship contenders. Of the top 12 then, seven made the Chase. After 11 races, that number had risen to nine drivers.

After the next three or four races, fans will have a good idea who'll be the top contenders this year.

The only question that will remain is: Can any of them beat Johnson?

Biffle, who finished second in points in 2005 and third in '08, believes he has as good a chance as anybody after his strong start. But will the improvements his team has made be enough?

"Definitely feel like we're gaining on them," he said. "We've beaten them a few times this year. Miraculously, I don't know how.

"... We feel like we've certainly gained on them, and we're certainly going to be able to continue to put pressure on them at these other race tracks (Phoenix, Texas and Darlington) where we feel like we're pretty dang good."

But are they good enough?