4.2GHz all-core is decent. An extra 100MHz is only 2.38% higher. It's barely worth considering really. Marginal gains at much higher voltages.
I'd just save the 4.3GHz BIOS settings and bust it out if you want to get a higher benchmark score or something.
I know with my i7-6800K, I can easily get it to 4.3 instead of its daily 4.0, but in that case the difference is 7.5%, which is actually pretty decent in CPU-bound scenarios.
For 100MHz, it's not worth it in the world of 4+GHz. Save on the power consumption, heat output and put less stress on your CPU and motherboard. 4.2GHz seems to be an ideal place on the performance/voltage curve for you.