The overclockers fro Xtreme Systems got their hands on an engineering sample of the Intel Kentsfield. Their quad-core processor was clocked at 2.4GHz with a 1066MHz FSB.
The topic is pretty long and fortunately the Dutch Tweakers.net analyzed the thread a bit. They noticed the processor performs roughly the same as a 2.4GHz Conroe when it runs one or two threads.
However, in synthetic benchmarks like Cinebench 2003 the processor really shows its power. The dual-core 2.7GHz Conroe scores a 873 and the 2.4GHz Kentsfield scores 1347 in this benchmark. When overclocked to 3GHz the Kentsfield manages to score 1649.