Celeron 566 & SY6VBA133

I am owner of SY6VBA133 MB. I just bought Cel. 566 Coppermine. MB officially supports Cel. up to 533 MHz, so my new CPU is beyond. spec. MB recognizes it, but it runs at 1.73 V. I read, that correct voltage should be 1.5 V. Am I overheating CPU? How can I find R E A L temperature of CPU, as BIOS measurement is 55 deg, winbond HW doctor says 35 deg and Sisoft Sandra displays 45 deg? What am I supposed to believe? CPU is running at 666 MHz, appearing stable.