not sure, but in real world "paul" testing methods, my friend has a 1.6a @ 2.13, and I have a tbird 1.4 @ 1.05 (cuz my mobo's kinda weird.... but that's a whole other issue) and my processor runs with a faster fan at about +5 or +7 degrees celsius higher temps then his overclocked 1.6a. He has a AVC sunflower p4 heatsink (available in the hot deals forum - forgot the site - for about 20 dollars), not sure if its any better. His is quieter, its a 70mm fan I believe. His case temp is about the same as mine, 22-25. Also, it might be a motherboard temp. sense issue, who knows.
I'm not sure why his is cooler than mine, could be the contact area being larger too? Beats me, all I know is it seems like the x.xA series p4 (northwood right?) seem to run cool (punny). Haven't heard of many/any problems with heat on the p4's
Good luck!