Seeing I just got a 7700k and tried both the maximus ix hero and the asus prime z270-a, I can say they overclocked exactly the same @5ghz (same vcore) but the hero overclocked the 3200 cl14 ram just by enabling XMP and on the prime I couldn't do CL14, only CL15.
Didn't try higher frequencies but maybe over 5ghz it will be easier with the hero.