Hi Nick! I don’t recall Jimmy or Frank playing anything string skippy. Caveat being I haven’t looked at the Frank footage in a long time but I don’t recall anything like that.
Personally I have no appetite for repeated wrist-extension, i.e. stringhopping, movements. Doing that fast for any length of time is an invitation to RSI type injuries and offers no benefit that I can think of when a true crosspicking movement will do the same job with no more stress or strain the “regular” alternate picking.
The other method for repeated downstrokes is the gypsy rotation way, and there are players like Joscho who can do this pretty fast:
https://troygrady.com/interviews/joscho-stephan/clips/arpeggio-min-gypsy-fast/
I was able to get good enough at this for about five minutes, just long enough to film a section for one of the Eric Johnson lessons:
https://troygrady.com/seminars/cascade/chapter-22-skip-fives/
To be clear, Eric doesn’t actually appear to pick all the notes in the “skip fives” patterns, but in tooling around with the fretboard shape I found that I could do two consecutive downstrokes really fast with a rest stroke / rotation approach that I think is essentially what the Gypsies are doing. I haven’t worked on it since, but it feels less strainy then the repeated wrist pecking motion of stringhopping. I can’t say why that would be, but that what was my impression.
Again, to be completely conservative, I’d suggest everyone avoid repeated pickstroke type movements since it’s basically double the abuse on the muscles and tendons for the given number of notes. We’ve already heard enough horror stories on the forum here to scare me off of these for good.