CPU Temperature monitoring software telling me different CPU temps

Hi, I'm about to overclock my Q6600 G0 (currently at stock 2.4GHz, 266MHz FSB, x9 multiplier) to 3.2GHz. (air cooled)

I have downloaded a few different temperature monitoring software: CPUID's Hardware Monitor, and SpeedFan, to check what temperature my CPU is on idle. I checked this on my BIOS as well.

The BIOS reads my CPU at about 43C and my system temp at about 36C.

The problem is, on SpeedFan, there are two CPU readings, one is currently at 22C and the other is at 32C. There are also two system readings, one at 16C and the other at 35C. I am really confused by this as you'd expect there to be only one temperature for each.

Then in HWmonitor, it's saying SYSTIN temp is at 16C and CPUTIN temp is 22C, however the individual cores are at about 38/39C each.

I've linked a screenshot showing my temperatures in each software, I've highlighted them as well.

Can anyone tell me why this is happening, and which of the temperatures is the actual temperature for both the CPU and system temp?

Thanks.

http://i.imgur.com/KlFmf.png

 

It's reading the temperatures from different sensors, some of which aren't as well calibrated or positioned in the right place.

I would use Coretemp to read the sensor from the CPU itself.

Argus monitor is another good tool that I find to be accurate and versatile

 

The motherboard software can also be good for reading temps. Asus AI suite is pretty good if you have an asus board.