agreed with most of ez2remember's points...
...except that the P4 doesn't REALLY have a larger contact area -- it has a heat spreader that protects the CPU from mech damage and actually adds another 2 layers (aluminum and thermal interface material) between HS and core. This actually decreases the cooling power of the HS!
What Intel also has in the P4 is all kinds of embedded tricks to cool itself down when no being pushed, a good thing. And a thermal senor located in a far corner of the core that reads as much as 15C below the highest point. Maybe not so good. So you and I see the monitored diode reading and shrug -- oh it's only 55C -- when in fact the hottest part of the core could be 70C. Deliberate? Smoke and mirrors? Hard to say, but I wouldn't put it past them. See page 2 of SPCR's Unique Heatsink Testing Methodology
There are 2 version of the 6000 BTW - cu and alcu. The copper version is better, for sure.
Aside from the 6000's big gap down the middle and the questionable clip, the big difference vs the 6500 models (for P4) is size: the latter are twice the mass, at least 25% larger in area.