Watch the Permutations of Root online guitar lesson by Brad Carlton from Guitar Lab: The Golden Arp
This lesson deals with options regarding the number of voices ringing at any given time. I'll start with a one note-per-string 2nd inversion E add 9 arpeggio on the top four strings. I'll then play a 5231 pattern by I'll vary what voices ring together. This demands great fretting hand independence so take it slow. This is a concept that guitar players frequently overlook so be sure to apply it to your playing.