northwoods are slightly faster under 3.6ghz where their short piplines work very well, the presscott has many more pipelines which benefit it more around 3.6+ghz. The norhtwoods also have 512kb L2 cache while th Presscots have 1mb. Presscotts all have 64-bite extensions, on all 478 though those extensions are locked. On 775 the 500 series have 64 bit extensions locked as well. (the only proof that presscotts have EMT 64 bit are the 501 series processors which have 64 bit extensions unlocked) Also some presscots have a multi drop trick, in whichteh motherboard sends a signal to the processor tellign it it has insufficient voltage regualtion for the chip, so the chips multi drops to 14x. On socket 478 the 3.2e C0 stepping SL7B8 is the only presscot 3.2 to have this capability, the 3.4es also shoudl have this. Also northwoods and presscot have difffernet stepping, which just indentify the processor revisions. In order of worst to best for ocing: Northwood: C1, D1, M0 (rejected EE) Presscot: C0, D0, E0 . Also their is the irwindale core (600 series) which is just a presscott with 64 bit extensions unlocked and an extra 1mb L2 cache.
Northwoods seem to not be able to reach 4ghz as easy as prescotts, the highest northwood OC ive seen is 5.24ghz, the highest presscot ive seen is 7.3ghz. In general prescotts OC better. Also northwoods have a safe zone under 50c and prescots under 60c taken that prescotts do run hotter at the same clock speed as northwoods.
Northwoods also have a stock vcore around 1.5v prescots areound 1.38v. Also all prescotts are 90nm (thats 90nm between piplines) and northwoods 130nm, this is also a reason for better overclocking, we shoudl see even higher clocks with the P4 65nm chips come out.
Jsut a little of what ive seen over the years.