CPU Spead Readings?

[geowal19]

I've got a an E7400 2.8Ghz. In the bios the speed is read at 2.8ghz in CPU-Z, OCCT and EVEREST it says it's at 1.6ghz but the performance is good and the tempreture readings are realistic in EVEREST 36C no load. What's going on?

 

[geowal19]

Yeah but I don't want to do this, I don't pay the electric bill and how much difference is it?