It depends on whether it's a Northwood "C" processor or a Prescott "E" processor. The latter will be warmer. At the time I was OC"ing those Northies and Prescotts, I was only measuring tCase temperatures. With stellar air-cooling, at room-ambient of around 75F, my over-clocked Prescott (20% OC) would peak at load to between 40C and 43C.
With lesser cooling, a similarly OC'd Northwood in the "family collection" may peak out at 75 to 80F room ambient at between 43 and 45C. You can normalize these observations with a linear compensation for room-ambient differences.