The section that comes in at just before 3 min in both vids is something else.
Edit: Here's a description of that section:
The initial two-note motive that Rzewski expands with hand and forearm clusters gradually morphs into a boogie-woogie bass, but without the swing so as to still effect the static drive of the cotton mill. Over this bass line he introduces the Winnsboro melody but in an extended, rhythmically disjointed manner so as only to give a hint of the flow of the melodic line. The right hand then picks up the bass line but a minor ninth above the bass to continue the drive towards alternating ninth chords in both hands that climax in alternating black and white key clusters at the extremes of the keyboard. Even throughout the darker cluster sections and the final climax, Rzewski maintains motivic unity by referencing the descending third sequence from the beginning of the Winnsboro melody.
A really nice report from the AHRQ on searching for grey literature (and some other tangentially related things), with corresponding empirical evidence to justify the effort.