Robert Hallock, Senior Technical Marketing Manager at AMD, has explained on Reddit (and copied below) that AMD pretty much squeezes all the performance out of every single Ryzen 3000-series processor, leaving little headroom for manual overclocking.
AMD has always focused on maximizing the performance from its processors for the end-user. According to Hallock, that's the primary reason why the chipmaker develops algorithms, such as Precision Boost 2, to automatically extract every megahertz of computing power from a processor. That way you're not forced to learn about overclocking to get the extra performance or worry about risking the warranty on your brand new processor.
From our own experience with the Ryzen 9 3900X and Ryzen 7 3700X, we can confirm Hallock's statement, and a couple of motherboard manufacturers have told us the same thing. For example, our Ryzen 9 3900X and Ryzen 7 3700X samples operated with an all-core boost of 4.1 GHz and 4.125 GHz, respectively, during our testing. Our efforts to overclock the chips beyond 4.2 GHz were futile. Overclocking extraordinaire Allen 'Splave' Golibersuch only managed to break the 4.1 GHz barrier with aggressive voltages and exotic cooling, albeit with early silicon.
While 7nm processors are certainly impressive, it's hard to ignore that both the 7nm process node and AMD's Zen 2 processor microarchitecture are still in diapers. They need their time to mature, and perhaps, in the future, we'll see processors with better overclocking headroom. There's also the other possibility that AMD has mastered the art of binning Zen 2 chiplets, leaving almost no space for extra performance.
Unless you win the silicon lottery and get an extraordinary Ryzen 3000-series chip, it looks like you're better off tweaking other aspects of your system than wasting time trying to overclock your processor's operating clocks. Hallock believes that overclocking your memory and the processor's Infinity Fabric interconnect yields more significant benefits.
I'm not sure what you're asking. Our boost formula is opportunistic based on VRM current, socket power, temperatures. Therefore: light workloads will have a higher boost, and heavier workloads will have a lower boost. This is the basic behavior of Precision Boost 2 we described in November 2017. This is the same boost formula used for all Ryzen 2000 Series CPUs as well: 4.3GHz peak for light threading, to around 4GHz for all-cores. No change year-over-year in how the boost behaves.
If you're asking whether or not all cores will hit the max boost clock: no. It will not do that, nor have we ever promised or implied that. We've been very clear for 1.5 years that the Precision Boost 2 behavior is a "curve" that tries to get the loaded cores to the highest possible frequency with respect to the aforementioned limits. Even with all cores loaded, the CPU can maintain frequencies that are hundreds of MHz higher than base.
The other goal of our engineering effort is to absolutely maximize the performance of the product out of the box. //EDIT: By designing algorithms that extract the maximum silicon performance automatically (e.g. Precision Boost 2) without asking the user to tinker or risk their warranty. So, no, you're not going to see a whole lot of manual OC headroom. That's just performance an average person--who doesn't know how to OC--can't access. Why would we do that? It is not our intent to leave anything on the table.
It's more beneficial to enable PBO, overclock the fabric, overclock the memory. But that's true of Ryzen 2000 Series, too.
-Robert Hallock, AMD Senior Technical Marketing Manager