Why am I getting mixed temperature readings from different programs?

I trust none of them unless I can set offsets compared to BIOS!

Speedfan is pretty widely regarded as being inaccurate, and I would generally agree that if the program wasn't supplied by the motherboard manufacturer, don't trust it. They're usually using an estimated value based on a formula. Speedfan's formula is based on what is generally considered to be some inaccurate assumptions, leading to inaccurate results.