Thanks KiLLa3D who sent me an email that references a finnish site called muropaketti.com. They overclocked a P4 2.2 Northwood CPU to a maximum speed of 3675MHz using liquid nitrogen (LN2 -196°C).
Heres a blurb from the English translation (scroll to bottom of the page to see) heh, the things people do to their CPU"s (an expensive one at that!)
The motherboard used in the tests was Asus P4B266 based on the Intel 845 chipset (DDR). There was a voltage modification on the motherboard which allowed the VCore to be raised as high as we needed. The memory module was Crucial PC2100 128MB and memory settings were the fastest possible (CAS 2 2-2-5).
We used a copper bowl on top of the CPU and poured some LN2 into it. It took a while until the CPU temperature started to drop and when it was cold enough, we started the test.
First test was run at 3300MHz (FSB 150MHz) and with no problem at all (VCore 1,9V). The next step was rather high but after raising Vcore to 2,05V Northwood worked stable at 3520MHz (FSB 160MHz). We went on with the tests and finally hit the limit.