Thanks for the advice! I am on AIR, using a "dark Rock 3" for the CPU, which I think may not be best for this Ryzen 3900X due to "not optimal" mounting pressure (the instalation system is really weak for the 3 series) I would like to try a Noctua NHD15...If you're cooling with air then try to reduce case temperature. If you're cooling with an AIO then pulling air from outside of the case through the rad. A difference of as little as 3*C in the ambient air might be all that's needed to get you to that 4.2GHz mark from 4.17GHz.
If you can't improve cooling then try adding just a touch of BCLK. Something like 100.4 gets that 4175 to 4191 and 100.6 gets it to 4200. Though you may find that if you're running 1900 FCLK then using 100.6 BCLK will put you at or past the edge of stability. I can't POST with anything higher than 100.6 with FCLK at 1900.