very nice article you made here.. I did knew and know what harmonic mixing is and having the experience from the field in many different ways as a dj (resident / booked artist) i can tell you that these ''rules'' are completely bullshit and nobody cares about it unless someone is a an operah musician or so.. because: A set doesn't need to be perfect and definetly everyone needs to fistpump on the set. this way of thinking with harmonic mixing makes dj;s restricted in their creativity in many ways because they follow ''rules'' while a good dj doesn't know rules other than beatmatching perhaps. Also nobody hears it anyway and if it is hearable that a key is different, then a pitch up already puts it in a different key... also harmonic mixing is something for non beat music with long chords and spheres, and a key is a key but which one? most songs are in an f or A / f# or F key depending on the style.. but what is a key? if a dj tries to be perfect then that dj should use ableton for live / presynched sets or priorly will mix in the more quite parts in the songs... finally i can tell you that a dancing crowd is the only positive sing that is needed to know if people enjouy... thats what is the main of a party... if everyone sits what is the purpose of a dj then (at partys) ;) good read, good blog and i hope my respond makes sense to you... like avian here, i used to have sets that range from 75 up to 150 and above sets too, mainly have spinned music club dance house electro.... with longs and short breaks, buildups etc... so harmonic mixing i would for all just advice to not think about it too much and keep the play the play