One of the most important exercise is to play stacatto, which you can apply to any piece you are dealing with and to scales (scales studies)I use to alternate between stacatto and legato/portato playing, using the same speed for both and slowly incrementing that speed.You will notice that in stacatto you cannot play so fast as in legato/portato; if you play legato fastest than you can stacatto, probaly you are playing bad and missexercising. Only once you achieve the maximal speed in stacatto, go beyond that speed in legato/portato.
I don't quiter understand your post. It sounds like you are both saying that if you can play legato faster than staccato you are practicing wrong, but then you also say that you should go beyond the speed you can play staccato when you play legato. Can you clarify?
… for me speed problems are always brain problems
I would suggest parallel sets as a way to learn to think quickly.
Can you expand on what parallel sets are?
Practising slowly does not work? That is usually what solves the problems for me.
Measuring the arc of your hand with a protractor, the force produced by a fortissimo in newtons, and the like is not entirely necessary.