On tonight's (Dec. 5) episode of 'X Factor,' the top six contestants faced a daunting series of new wrinkles in the competition. Who rose to the challenge, and who runs the highest risk of going home?

Tonight was a double elimination night -- and a double performance night, too, as each contestant had to tackle two songs: One acoustic number, and one chosen by the viewers. Going unplugged poses its own risks (as Demi Lovato put it in the intro, "Some will rise to the occasion, some will fall under pressure"), but leaving song selection up to the unwashed masses is even scarier. Let's look at how our would-be 'X Factor' champs fared:

CeCe Frey: Demi's lone remaining contestant took the stage in a tasteful formal gown after an enthusiastic intro from her mentor, who insisted she "has what it takes, she's relevant, she's beautiful, she's a sweet girl" -- and while her performance of Lady Gaga's 'Edge of Glory' was a bit wobbly in spots, it was also refreshingly subdued in comparison with her previous outings. L.A. Reid, who revealed his disdain for Frey in the pre-taped intro segment, was forced to eat his words at the judges' table, telling her, "Sometimes we get it wrong, because I'm starting to become a fan." Britney Spears disagreed, saying "It was just good for me," while Simon Cowell didn't mince words, telling her, "I don't think you're worth a $5 million recording contract."

CeCe's audience-chosen number, Katy Perry's 'Part of Me,' found her returning to her leopard-faced roots, vamping around the stage in big hair and bright clothes while singing along with a light show and dancing troupe. Sadly, all those pyrotechnics drew another mixed response from the judges; L.A. said he felt "like a windshield wiper" after going from loving her last performance to...well, not loving this one. As a parting shot, he added, "If there were ever a karaoke performance, that was it." Britney, however, loved it -- and as Demi pointed out in her comments, "If the Princess of Pop is sitting here saying you did a good job, then you did a good job."

Emblem3: Even before Simon could introduce his teen vocal trio, Demi grabbed the mic and predicted they'd be singing a "very predictable song" -- and while we might not have been able to outright predict that they'd perform Bruno Mars' 'Just the Way You Are,' it certainly didn't represent the most exciting or unusual choice for the group. Sitting on crates and taking turns singing lead on the verses, they displayed their usual tight, albeit safe harmonies, but even their most ardent fans would have to admit it's easy to see why Demi frequently describes herself as "bored" by these guys. She echoed her previous criticism, telling them "You guys did great" before explaining, "It wasn't the best. I used to really love you guys, but I feel like it's a downgraded version of the Jonas Brothers [from] five years ago." Simon quickly fired back, telling her "That was incredibly dumb, what you just said," before turning to his proteges and saying, "The pressure to deliver what they just did -- these are young guys, and the pressure's on them now. You're amazing."

In the show's second hour, Emblem3 returned to cover Alphaville's perennial prom favorite 'Forever Young,' hitting all the expected marks with a rendition that emphasized the song's huge, emotional chorus without actually doing anything new with it. But that was more than enough for most of the judges: L.A. said they "nailed it," Britney called it "a superstar performance," and Simon crowed, "I think you've been really, really good tonight. Emblem3 have landed." Demi's one caveat? They don't work the stage enough, to which Simon responded, "That's just a silly criticism."

Fifth Harmony: Repeatedly criticized by L.A. for never actually singing harmony, the girls faced a tough week of preparations without group member Allie, who was out of town attending her grandfather's funeral, and a bewilderingly safe song choice from Simon: Adele's 'Set Fire to the Rain' (seriously, hasn't every Adele song been covered to death on the singing competition show circuit by now?) Although Allie made it back in time, giving Fifth Harmony at least one happy ending for the week, their first performance met a darker fate. True to form, they neglected to actually sing harmony, something Reid delighted in pointing out from the table, much to Simon's chagrin -- as he put it, "It's pick on Fifth Harmony Week again, because that was really unfair criticism...I think they deserve a shot in the semi-finals next week."

If their first trip on stage was met with mixed reactions from the judges, Fifth Harmony faced no such problems with their follow-up performance, a fan-chosen cover of Demi's hit 'Give Your Heart a Break.' A terrific choice for the group, 'Break' gave them each a chance to shine individually while leaving room for them to showcase their vocal blend -- and even work in a little harmony, something L.A. noted appreciatively during his remarks from the judges' table when he called it their "very, very best performance." Demi agreed, graciously saying, "I think this song should have been your song. You sounded so beautiful on it...better than the original. It was energetic, it was fun -- I think that Simon actually did a good job this week."

Carly Rose Sonenclar: Last week's first-place winner was handed an unusual song choice by her mentor: Justin Bieber's 'As Long As You Love Me.' It befuddled L.A. Reid, who helped make Bieber a star; as he told the cameras before Carly's performance, "I don't know what she's doing -- I don't get it." Carly seemed to share L.A.'s skepticism, admitting, "I love it, but it's not acoustic, that's for sure...it's my biggest challenge yet." But as Britney reminded her, "If you make it your own, it's a home run." And that's pretty much exactly what Carly did, delivering a thoroughly unique rendition of Bieber's hit that drew unanimous praise from the judges' table.

Having set that high bar for herself, Carly came out in the second hour and shattered it, taking the fans' choice of Beyonce's 'If I Were a Boy' and claiming ownership of the song with a remarkably assured performance that showcased her impressive range and nearly flawless control. Anything can happen over the next few weeks, but at this point in the contest, young Miss Sonenclar is clearly the one to beat.

Diamond White: She narrowly escaped elimination last week, something she admitted "hurts" in the pre-taped segments, but said gave her added motivation -- as she put it, "You have to fight for your life." Britney went back to the past for Diamond's arsenal this week, giving her James Brown's 'It's a Man's Man's Man's World' -- a tough song, and one she'd already performed, making it twice as hard to impress the judges. She managed to do it, despite the arrangement sitting at the upper limits of her natural register (something Simon referenced when he referred to vocals as "a little bit screechy in parts"); as Britney told her at the end of four solid reviews, "You not only nailed it, you destroyed it."

Diamond returned later to sing the fans' choice for her: Rihanna's 'Diamonds.' While we shed a silent tear for the fact that Paige Thomas wasn't on hand to take this one, Diamond acquitted herself admirably, singing with tons of emotion and hitting all the right notes -- albeit perhaps with not quite as much power as the song demands. "I really like you. I really like that song," admitted an apologetic L.A. Reid. "Unfortunately, I didn't love your rendition of it." Simon's remarks also seemed to strike an ominous note -- "It's just your luck that you're in a very, very competitive top six," he warned. "Overall, I think you've had a good night."

Tate Stevens: L.A.'s final contestant finished in second place last week, just a few votes behind Carly Rose Sonenclar -- but this week, his fortunes seemed to falter thanks to what Simon deemed "not a great song choice, unfortunately": Bon Jovi's 'Livin' on a Prayer.' Delivering a slow, stripped-down version of the band's signature hit, Tate's command of the melody sounded just a little bit off, particularly in the chorus, where he shied away from the climactic high notes and settled for the low harmony. Demi called him on it, saying he "skipped out on...the best part of the song," while Simon called doing 'Prayer' during acoustic week "like taking a goldfish for a walk -- you can't do it." Reid, of course, disagreed, telling Stevens "You've done everything to support your family, and you're finally doing something for yourself. They stand behind you, and I stand behind you."

After coping with a couple weeks of questionable song choices from his mentor, Tate was given a number squarely in his wheelhouse for his second number of the night: the Garth Brooks hit 'If Tomorrow Never Comes.' Asking him to do nothing he can't or shouldn't do on stage, the song played squarely to his strengths as a performer, and he was rewarded with a round of unanimous praise from the judges. "Now that felt like a Tate Stevens performance. That was brilliant," said Britney, and Simon added, "Welcome back to the competition. I'm really happy you've come this far...I think we're going to see you next week, 100 percent."

Now that the judges have had their say, it's time for the voters to make their picks. Who will be sent home in tomorrow's (Dec. 6) double elimination show? Tune in to find out.