Hi,
What do you use to put 100% load on cpu? Some apps wont put the same load on both cores. Theres also a possibility that one sensor is getting "stuck", i read something about it when i had same thing with my e5200, but indeed it was the apps fault because when i used prime95 than both cores were within 2C from each other at all time. And Id say 39C under load is more than reliable