I have a AMD x4 620 installed in a gigabyte 770 board. The cpu multiplier when set to AUTO in the bios has the cpu running at 4x. I didn't print out the CPU_Z page when I first ran the computer about 2 months ago, but my memory tells me Auto gave me a 13X multiplier then which is the default. I don't know what has happened to change it. Suggestions?
I believe what you are seeing is the idle clock multiplier (4x = 800MHz at idle which sounds about right if my memory serves me properly :-p) which is what you will see when you are not utilizing your CPU very much. The 13x Multi which you've also seen is the default loaded value which is 13x = 2600 MHz, which IS the stock clock for your Athlon x4 620. So really, both are correct and the only thing that changed was how much work your CPU was doing at the particular times.