You have a Core 2 Duo, so get yourself Intel TAT. A temperature-reading utility from Intel themselves. Try that first. Speedfan might not like your motherboard, and may be reading the wrong sensors.
If in fact you find you your CPU is going above 65C under full load, you have a problem, as 65C is the maximum operating temperature for Core 2 Duos. Above that, and you are damaging your processor. There are 3 main solutions; re-seating the heatsink with Artic Silver 5 or Zalman STG-1, buying more fans for your case so more cold air is blown in and warm air is actually being removed, and/or buying a new heatsink.