Watch the Speed Picking: Level 3 online guitar lesson by Chris Buono from Guitar Gym: Speed Picking Workouts
Workout #1 takes on the C major and C natural minor scales in three-note-per-string chunks in sextuplets. Granted, sextuplets will be a bit nasty at the high tempo (130bpm!), but don't write this off before playing the workout. It's purposefully set up in a way that not only gives you the needed resting period in-between phrases, but also flows real nice as you play the three-note-per-string sequences twice only to land on the starting point on the next downbeat. Try it and you'll see what I mean.