The short story goes like this. During a press overclocking event in late November, AMD got a Phenom II up to 6.3GHz with LN2 cooling. Intel immediately cried foul, and said that they were one in a million cherry-picked samples, and that they would top it.
There have been several back and forths between super-OC'd i7s and Phenom IIs, with the current records being a little in favour of AMD for quad cores. As you can see here, things currently stand at 5611Mhz for an i7, 6436MHz for a Phenom II. That said, Mhz does not equal performance, and this is not to say that the i7 won't get more work done at 5.6GHz than the Phenom will at 6.4Ghz... wait, this is silly. Neither can do much at that frequency other than make an overclocker very nervous, holding his breath and clenching certain lower abdominal muscles hoping things don't crash.