Help a noob interpret Real Temp score, please..

[LearninToBuild]

Here's my Real Temp CPU screenshot:

I've never seen the 40C on the left ever get higher. Even when I use Everest, one temp is 40 degrees, and the other two temps fluctuate from 27 to 35.

Please help me interpret the images in the screenshot, I'm trying to determine how cool my CPU is running. I have installed a Dark Knight heat-sink on it, and it has the thermal paste supplied with it applied correctly as the instructions indicated to. Why does thermal status only say "OK" instead of "good" assuming that's an option?

And in general is this a very good temp?