Thanks for the posts, everyone! It’s also discussed in Troy’s video with Joe Stump regarding economy picking (around 2:10, but to be honest I don’t detect it as much - maybe since those exercises seem to keep DWPS (side question … is that lingo now replaced by “USX”?)
Wow Shima and Filho are both interesting examples; seems like they’re using it even when staying on the same strings. For me it seems present ONLY when changing strings - looks like something fun to try to experiment with! And as speed goes up and I start going to elbow, my hunch is that the tension I feel is excessive compared to the common advice of “you’ve got to be relaxed!”
FWIW, the two riffs I am working toward with 1&3 nps groups are 150/155 bpm
(0:44 in case this doesn’t work - by Archspire) and
(2:08 in case this doesn’t work - by Spawn of Possession)
For both of these I can really keep up cleanly only to about 85%