isolate a single note from a fast scale and it will be very fast, to the point of being staccato. At a certain point the fingers know how to go down on the note well and it becomes more important to have a quick release so the fingers can 'reset'.
An idea:
forget the metronome, feel pick a scale and work at it for a good long session. Slowly until the fingers know automatically where to go, then you can speed it up by feel. When the fingers are automatic you will be able to think less of them and more of simply the notes. I found this 'musical' thinking much easier to get to high speeds cleanly.
This kind of practice session conditions the hand very much to that particular pattern. After concentrating on one scale for up to an hour you'll have difficulty playing another scale because the hands will be strongly conditioned to that movement alone
Not good for adaptability, but good for exploring the limits of speed.
I know many advocate the idea of short practice sessions, but I've found it's useful to stretch the concentration to longer sessions from time to time. If you can sit down and focus on one problem for an hour you will get very far into that difficulty.
Topic: Developing scalic playing