Does your case have side panel ventilation? The best way to cool a prescott is to have either a side panel housing that fits directly over the HS and the fan is inverted to blow out of the housing. Or have a housing that connects to the rear of the case to a case fan. I've found in my installations that when I invert the fan to blow out and through the housing, it cooled much better. Some will disagree but I go with what works.
By the way, what are you using to get the CPU temp's? BIO'S? 3rd Party Software?