SANTA CLARA – Left tackle Joe Staley, who called the Lions' defensive line "extremely overrated" following a win against Detroit earlier this season, has the opposite take on his Sunday opponent.

"I think they're the best of the bunch," Staley said of the Buffalo Bills' defensive line. "All four of those guys – all very, very talented."

That's notable praise considering the 49ers already have faced two of the most acclaimed defensive lines in the league, Detroit's and Minnesota's, and last week squared off against a Rex Ryan-led New York Jets unit that was supposed to present a challenge to the San Francisco offense.

Still, the 49ers were unanimous in saying Buffalo, which ranks 27th overall in team defense, would be the best test yet for an offensive line that is beginning to surge and assert itself as one of the best in the league.

The 49ers gained 245 yards on the ground in last Sunday's win against the Jets, the team's most since a 261-yard performance against the Arizona Cardinals on Nov. 29, 2010. They're averaging 5.4 yards a carry, second best in the league.

But quarterback Alex Smith has been sacked 12 times, tied for sixth worst in the league.

Still, it's slightly better than the 14 sacks the line had surrendered through the first four games last season.

"Big, strong and physical," said Bills coach Chan Gailey when asked about the 49ers' offensive line. "I mean, they're playing extremely well. They are a strong bunch. They're probably overall the best group we've played this year."

Right guard Alex Boone, who has made a seamless transition from tackle to guard this season, said the competition between the 49ers' offensive line and the Bills' defensive line will be the game's best matchup. He called it a "full-day sucker."

The Bills made one of the biggest splashes in the offseason by signing ex-Houston Texans defender Mario Williams to a six-year, $100 million contract.

Williams, who will square off against right tackle Anthony Davis, has only 1 1/2 sacks and nine tackles this season, and he is starting to irk Bills fans who are unhappy that his production has not matched his earnings.

The 49ers, meanwhile, say a more anonymous Williams, Kyle, is the top defender on the Bills' line. The defensive tackle, who will draw Boone and left guard Mike Iupati at different times Sunday, leads Buffalo with 3 1/2 sacks.

"Mario Williams has gotten a lot of press for a long time, but I think the best player is Kyle Williams," Staley said. "Very underrated player. He doesn't get the national press that the other guys do on that line, but he's a very solid, very impressive player."

In fact, several 49ers this week paid Kyle Williams the highest compliment by comparing him favorably to their own top defensive lineman.

"He's a lot like our Justin (Smith)," Boone said. "He's a hard worker, always trying to get to the ball, doesn't give up. It's going to be a full-day fight with him."

Offensive coordinator Greg Roman called Kyle Williams a "buzz saw."

"I think he leads their D-line in sacks and tackles," Roman said. "Really heady player, physical, doesn't have the length Justin Smith has, but similar style of play. It's going to be a handful."

Injuries – Despite saying all week that he would play against the Bills, running back Brandon Jacobs (knee) is listed as questionable on the 49ers' injury report. So are cornerback Carlos Rogers (ankle) and nose tackle Isaac Sopoaga (knee, ankle).

Linebacker NaVorro Bowman (shoulder) is probable.

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