I've not used Y-Cruncher for my stability OCs (I normally use OCCT), but I wil try it in two of my systems (1700X and 7800X).Which is even higher than I've observed. The majority of 1700 chip overclocks I've observed on forums are around 3.8Ghz and lower. 4Ghz @ 1.440v and Asus Real bench stable is quite the achievement.
Edit: You do have Ryzen, right? Try the Y-Cruncher avx stress test to see where your true clocks should be.
Meanwhile, whats the average Skylake-X true clock achievable with OC stability tools such as OCCT, Prime95 or Y-Cruncher?