There could be several additional causes for temperature differences, like you've mentioned, radiator placement and contact through thermal paste, as well as ambient temperature differences. Of course, even different CPU samples could result in thermal offsets.
As I could gather from both test results, they are all well in the safe temp area so there probably is no reason to worry. If I remember correctly these chips can reach 80+°C without any major issues.
It's probably best if you get an answer from Krešo on this matter, for some additional and more precise info on test variables/circumstances.
Btw I like that quality 250W HDPlex power supply you've got there in your test bench, and I've been seriously planing on getting one a year ago, but eventually I ended up with an SFX sized PSU. Are you satisfied with it ? Any practical drawbacks or flaws?