The Coolaler.com website managed to get a hold of and test the one and only Core 2 Extreme quad core QX6850 processor.
They played a lot with it, since they managed to get it from the default 3 GHz to 4,800 MHz, with LN2 of course. The default speed of QX6850 is 333 MHz Bus speed with a 9x multiplier which ends up at 3,000MHz on a 1,333MHz FSB. The QX6850 will be the only processor called Core 2 Extreme with 1,333MHz FSB, and probably the last stand of Intel on 65nm. It comes with total of 8 MB cache, 2x4MB to be exact since it is two dual cores taped together inside one chip.
Super PI 1M test on QX6850 with Vcore set at 1.56v and clocked at 4GHz (364x11=4,004MHz) with DDR2-1092 5-5-5-15 ended for 12.844s.
The rest of the Super PI tests and screenshots can be seen here on Coolaler.com, and the validated 4.8GHz OC can be found here.