you can run a sensor test and it will give you a full range of temps at various loads. you can then see which sensors are more sensitive.
I have two sensors on my i7 920 that are more sensitive than the other two. They are lower than the others when idle and higher than the others under full load.
What I ended up doing was just making some small calibration adjustments to make the sensors more even under full load.
It is also possible that your CPU cooler is only making partial contact with the CPU.