There may be some applications where the Prescott is able to just edge over the Northwood core but I think most reviews have shown that even the larger cache cannot overcome the negative impact of the 30-stage pipeline in Prescott. Most benchmarks place the Northwood at or above the Prescott...which also runs hotter. At this point in the game I would suggest picking up a Northwood. Cheaper, faster and cooler.
Things will likely change once Intel can improve the 90nm process and scale Prescott to higher speeds. It does tend to perform faster than equally clocked Northwoods once you surpass 3.4Ghz.