There seems to be some nonsense with the Ryzen CPUs where the reviewers are given golden sample chips that can hit higher than realistic overclocks. I have an 1800X and it's a horrible overclocker. I can't even get 3.9ghz out of it. But according to AMD, 4.2ghz should have been easy. It's good that we're getting some actual user experiences online. I was interested in the 2700X if it could hit 4.3ghz. I'm starting to realize that it can't unless you get a golden chip.
This hasn't been my experience.
I picked up a 1700X back when that first came out last year. 3.9GHz was easy. I eventually got 4.0 GHz out of it, though that took a LOT of tweaking. That was on air cooling (Noctua U12 cooler).
A few months ago, I dropped in a 2700X into the same setup and sold off the 1700X on ebay. The 2700X easily OC'd to 4.2GHz. And likewise, some extreme tweaking eventually made 4.3GHz possible - though the temps are very borderline for my liking.
On the 2700X, I wound up removing the overclock because Precision Boost did almost as good by itself. But my results were definitely in line with reviewers, who got 4.2 (HardOCP) on the low end to 4.4 (Guru3d) on the high end. HWBot has the average 2700X OC (on water) as 4285 MHz. So expect to land right around 4.3, +/- 100MHz with good cooling.
Now, AMD never claimed that first gen Ryzen was going to get 4.2 (except maybe the cherry picked 1900Xs). So I'm not sure where you got that. 4.0 was the typical expected result, +/- 100 MHz or so. Maybe a bit less on some crappy 1700s.