Dear Opus and Nicco:
Perhaps I didn't express myself in the proper way. As a matter of interpretation, fast
tempi are a choice, not a difficulty. Let me give an example.
When I study a piece, I generally start at a moderate to slow pace. There is no rule: it's just the speed I can control my hands, their coordination, and my expression and interpretation. As I get acquainted with the piece, I like to explore it in many ways: dynamics, articulation, touch, color, sound, speed/agogics, and so on. Thus, the piece gets several "versions" before I am satisfied with it. Working this way, I never did struggle with metronome: if I find some kind of speed wall, it's just a matter of patience and time, as I did write before.
In the other hand, I must agree that faster
tempi sometimes introduce problems. But think a bit: the problem is not the speed, but what you have to do.
Example: when I did study Beethoven's opus 2/1 fourth movement, I had a major difficulty with the LH arpeggi, because neither the speed nor the arpeggio itself, but the movement of the LH from one octave to another. It happened no matter how slow or fast I did try. So, when I figured out the proper arm change, this issue was not a problem anymore. And play it fast was not a concerning point either. Another example that occurs me is Chopin's 10/1: the same question, just in the RH.
Faster tempo causes greater diffculty, of course, there is no need to deny it, or claim you can play any speed you want with the same articulation and precision as with slower tempos.
Nicco, you wrote about articulation and precision in different speeds. In spite the fact I don't want to argue with you, since if that's your approach I do respect it, I must disagree with you. I never use the same articulation in different speeds. As any of the other interpretation choices, it changes from slow to fast. For instance, the kind of
staccato I use for a slow phrase is very distinct of a fast one (not only musically, but basically in terms of movement).
About precision, I should say that - to me - it's again not a matter of technique, but of focus and knowledge of the piece. When I know a work truly by heart and concentration helps, play it fast it's something natural; otherwise, it's just impossible.
Best wishes!