So um, who’s left who can beat Notre Dame?

Heading into Week 6, S&P+ gave Notre Dame a win probability of 80 percent or higher, with a projected winning margin of 14 or more points, in five of its seven remaining games. The Irish had a 21 percent chance of reaching 12-0 and a 59 percent chance of losing one game at most.

You could even say the Irish were undervalued, since they’d appeared to become a different team when quarterback Ian Book took over for the struggling Brandon Wimbush in the starting lineup, and S&P+ still gives the early Wimbush games equal weight.

Brian Kelly’s Fighting Irish moved to 6-0 with a 45-23 win over Justin Fuente’s Hokies.

Facing the most hostile road environment of his young starting tenure, Book responded to the challenge. He completed 25 of 35 passes for 271 yards, two touchdowns, and an interception; he also got help. After his pick, the Notre Dame defense stiffened and held the Hokies to a field goal, as they did on two other first-half scoring drives.

He also got help in the form of two lightning bolts. In the second quarter, Khalid Kareem stripped Tech quarterback Ryan Willis, and Julian Love scooped up the loose ball and raced 42 yards for a score. And in the third quarter, backed up near the end zone, Dexter Williams took a handoff left from Book and exploded past perfect blocking for a 97-yard touchdown. The Irish scored the first 21 points after halftime, turning a one-point lead into a comfortable margin.

In three games with Book as a starter, the Irish have beaten three power conference teams — Wake Forest, Stanford, and Tech — by an average 24 points. Based on last week’s S&P+ ratings (which should become even more favorable to the Irish when they are updated on Sunday), here are the remaining win probabilities:

There are only two true road games left. There are plenty of upset opportunities there — Pitt has scored CFP-level upsets in each of the last two years, Northwestern has no problem building leads on good opponents (and a lot of trouble holding onto them), FSU is improving, Syracuse nearly beat Clemson last week, and USC still gets to play Notre Dame in the L.A. Coliseum. It’s not a cakewalk ... but if the Irish maintain their current level, this is a schedule they can very much handle.

We’ve spent a good portion of the season talking about college football’s big four: in some order Alabama, Georgia, Ohio State, and Clemson. And to be sure, all four of them are still in very good shape for a playoff run. But since the QB change, Notre Dame has matched these teams’ level. For all intents and purposes, the big four has become the big five.