Wow that is fantastic  , what is the voltage btw?

Your is Ryzen 5 which variant?

Yaya, exactly happened on mine too, when full load the different so significant, i don't know which is correct? 
Not sure have you run some stability test or not, if u did so then 1.244v is quite low running at 3.9ghz, could be golden chip 
Btw what DDR4 are you using? Mind to share what speed its running?

Try going 4ghz with 1.3v under stresstest? If sucess, i think ur r5 1600 is the best golden chip among all.
I saw oc user database that only about 5 user can get  ryzen 7 run 4ghz with 1.3v @@

Not bad ya  , but wonder why the cpuz software shown the weird voltage, if really 1.6v sure fried the cpu already 

In order to check whether your pc is stable or not you should try to run aida64 stability test, just my2cents

Stability test varies.

Simple one, use Realbench run 15 minutes enough. AIDA64 also can but I don't know how good it is.

Want tougher test go OCCT 1 hour.

Usually i let it run at least 30mins, but u need to keep monitoring the temp, if it shootup really high then need to stop

Sorry write wrong. It's 4Ghz.

It takes far less time when you start high and slowly drop the voltage.

4Ghz with 1.45vcore is ok. This is to test whether it can run on 4Ghz.

If at 4Ghz with 1.45vcore still not successful then not good already, continue dropping speed until stable. After that, maintain the speed and drop the vcore until stable.