Expreview has managed to get their hands on a retail 45nm Core 2 Duo E8400 CPU and they've had a play with it to see how far they could push it; and it looks like this 3GHz CPU is a great overclocker, as they've pushed it all the way to 4.5GHz.
However, this was using watercooling and not the supplied Intel stock cooler. As you'll see from the pictures, the cooler Intel ships with these new CPUs has a heatsink that is only about half the height of the previous generation of coolers and the copper core is gone.
There should be a lot more benchmarks popping up of this new CPU which should launch any day now.
You can find the preview here