Ok, there are several things to go over here... First of all userbenchmark is pure garbage, just a steamy pile of..... There is no easier way of saying it, but it is a benchmark that both AMD and Intel Reddit have both banned because it is so extremely biased toward Intel based systems. Put simply it is the worst possible benchmark to use even though it is usually the first thing you'll see Google regurgitate when you do a search of CPU performance.
You would be much better off running benchmarks like Cinebench, Blender, Performance Test, PC Mark 10, 3DMark (Firestrike, Time Spy, etc..)... If you are running a monitoring app while running userbenchmark you probably aren't seeing accurate frequencies to being with, but the above mentioned benchmarks will all show you a much more accurate picture. With that said, the R5 2600 has a base clock of 3.4Ghz and a boost clock of 3.9Ghz. Therefore any boosting behavior above 3.9Ghz is just extra performance (ie overclocking) above what AMD has specked the processor to. In your post you say that your processor never turbos past the base speed but you quote the base speed to be 3.95Ghz which is actually better than the boost frequency for the 2600.
There is also two main "schools" for overclocking Zen+... There is precision boost / precision boost overdrive, and there is manual overclocking with a set multiplier. If you are using precision boost and PBO then you should be using a negative offset on your Vcore and the overall obtainable boosting frequency will depend on load / power / heat and your processor will only reach 3.9Ghz (maybe a little better) boost on a single core in light loads. If you are manually overclocking by setting a multiplier then you will probably be using a set Vcore or a positive voltage offset to give your processor more voltage to be able to run at 3.9, 3.95Ghz all core. If you are running a manual overclock and a set multiplier than your processor won't really "boost" it will simply go directly to your set overclock under load (if you are running with an offset Vcore voltage and Ryzen balanced power plan you may see the processor run with lower voltage and a lower frequency at idle but under load will go to your set multiplier there really isn't any "boosting" with a manual overclock).