I don't know if everyone's does this, but my board and some others will report 7-10°C lower (I use speedfan) after a warm reboot.
Speedfan will report 42-44°C Idle on cold boot, then whenever I do a warm reboot (even right away or hours later) speedfan will give 34-36°C Idle. I think this is getting fairly close to the actual temps.