If your using the Arctic Cooler 64 you shouldn't have a problem if its installed correctly. I have a 90nm X2 5600+ OC'ed to 3Ghz and I never see it go above 55. Right now its at 36C and 40C for both cores, and I didn't bother to remove the Arctic Cooler Thermal compound as I did a bit of research. In some cases, Arctic Cooling MX-2 thermal compound has beat AS5.
That is read using core temp which I think is a nice program as you can check log files and record temps from the CPU.
If I where you I would buy some AS5 and reset the heat sink because that doesn't sound like its on very well. When I installed mine I had a fear I was going to break the motherboard. When I finally got it on if looked like there was 300 pounds of pressure on that little thing.