For me, CoreTemp is the most trustworthy tool for actual die-temp reading. A very good way to check is to undervolt your CPU at stock or even below-stock speed. Say, try something like 1.2V @2.0GHz. You will get below 30C idle and below 40C load temp, or something like that. And as frequency goes up, and as you give more voltages the CoreTemp responses to the change very sensitively.