I set a timer and tried this for 30 minutes tonight 140s okayish but 150 a mess , I had to use the metronome to give me an idea of how fast. Was able to do 4’s over a caged major scale last night at 96 to 97bpm sixteenth notes and after this tonight had trouble at 90bpm. I dont Know what to think about this , wether to keep normally practicing string crossing stuff until I can get that up to 110 or higher or to devote more time to this. Common sense says to practise around the edge of your previous ability and push to gain an extra bpm or two over time . Perhaps I did wrong trying to practice with the metronome like he said, but at those speeds it would be easy to mistake 144 for 154 etc.
So is this bogus advice? I know the old saying that you can’t learn to run by walking fast which makes sense , but then there is the saying practice makes permanent so if you practice fast and sloppy you may end up playing sloppy .