Silicon Lottery sells specifically binned CPUs that are guaranteed to reach all-core overclocks. When you buy a normal CPU you have no clue how well it will overclock, it is really a silicon lottery (see what I did there). When it comes to the AMD Ryzen 9 3900X Silicon Lottery has stated that only 6% of the CPUs they tested will reach a 4.2 GHz all-core manual overclock. It seems it is quite hard to get extra all-core performance out of AMD’s Zen 2 architecture and that very few Ryzen 3000 CPUs are capable of high, and stable overclocks.
The Ryzen 9 3900X will boost up to 4.6 GHz, but that is only on select cores. This is made possible thanks to AMD’s thermal, power, and frequency boosting algorithm. Once you start manually overclocking, all-core max clock speeds are very hard to achieve, especially at a Vcore of 1.250. We actually had to crank up our Vcore to 1.40V when overclocking our Ryzen 9 3900X, this is not something we would suggest for a 24/7 overclock.
Silicon Lottery is selling the binned 4.2 GHz guaranteed Ryzen 9 3900X processor for $840, which is quite a lot to pay for a processor that has a MSRP of $399. Silicon Lottery also has a QVL for this processor which lists motherboards they would suggest running it on and a 240 mm AiO.