Distortion at Peak Dynamic Levels

Then tracking force may not have been the issue. Decreasing VTF moves the tangent point of the stylus to the grooves. That's because the cartridge suspension has a spring rate- less load equals less deflection. So the stylus position relative to the pivot point of the tonearm just changed. Different stylus shapes can tolerate more or less the error in the tangency to the record groove. Of course, with a pivoting tonearm, the tangency error can be 0% at only two points and if the set up is off a bit- to the point that error exists at all positions on the record, then the sound can break up even worse at certain areas on the record. Additionally, the VTA of the stylus changed too. And that could have changed the sound as well. All of the settings are inter-related. When I set up a new cartridge I start with VTF, then set VTA then set overhang (tangency point). I play some records and if I need to go back and make small adjustments, to VTF or VTA, then I recheck overhang.

Hmmm... it would make more sense if your downforce had been too low, as that can allow mistracking during challenging passages.

Still, some of the factors Tonywinsc mentioned may be involved. Or perhaps the excessive downforce took the coils so far out of alignment vis-a-vis the cantilever that certain frequencies were being distorted.

I'm guessin' wildly here! In the end, if it sounds good then it probably is. Enjoy the music.

The Shure ERA IV disc does not use artificial test tones. It has a variety of instruments, that cover various segments of music's bandwidth, recorded at incrementally increasing levels. It's a useful disc, if one is interested in testing one's trackability. To each his own!