Sorry just a typo the 640 max temp is 71°C.
I also have had doubts about the reported temperatures so I have a couple of hardware sensors installed in my system. These show that on my PC (which also runs a beta BIOS) that CoreTemp, AMD Overdrive, and Everest are between 5 - 8°C out. EasyTune6 reports the temps pretty accurately. If it was a BIOS issue this would also report inaccurate figures.