Thanks for posting these! I think there are two issues to sort out here.
One is just the motion itself. If you’re saying you feel speed limited at this speed, then we can try and figure out what you’re actually doing, but that’s kind of beside the point because you should be able to move a little faster than this. Have you watched the Pickslanting Primer wrist motion chapters for both USX and DSX? Were you able to do either of them on a single note, single string? Have you tried the rest stroke approach and did it help? If you haven’t done those things yet, definitely give those a shot and let us know if the results are any different.
Two, I didn’t notice this the first time, in some of these clips, you’re doing something I call “displacement”, where the picking hand picks a different number of notes per string than the fretting hand is actually fretting. This is a common mistake where the picking hand tries to simplify the phrase to even numbers of notes per string, either 2, 4, or 6, even when the fretting hand is fretting 3 three notes. This allows the picking hand to use a single-escape motion, which is simpler. Of course if that’s not what you’re actually fretting, it can sound unsynchronized.
I point this out because this isn’t just a synchronization problem. It’s your hand telling you it wants to use a specific kind of motion — the one you’re best at. And notice, we don’t see this problem in the very first clip here because — get ready — that phrase actually has an even number of notes per string. It is a USX phrase. So the hands stay synchronized.
So… perhaps when you go your fastest you only really have learned a USX motion so far. That’s not a problem. Learn to recognize this by feel and work on some awesome USX phrases. Try to smooth out the motion with rest strokes and accents, and check out the Primer chapters on USX motion. Then try to link up longer patterns where you always have an even number notes, like this one:
I like longer patterns so you can get going and stay going, and try to feel those accents. The goal here is to unlock more speed and smoothness by being aware of the USX motion you are making. Keep trying this different ways to see if you can go faster. Again, the rest stroke may help to keep the motion in a “straight line”, which is the fastest way to move.
Let us know how you make out.