The only thing I disagree with is that nail shape affects more the arpegio and tremolo stuff than picado (because you can push through a bad shape). Also you can in fact increase that single finger pulse speed overtime (I did but it took a long time using metronome), and the thing about coordinating two fingers to get closer to your "limit", is how fast you can SAY verbally the rhythm you want to play. Again I supply Paco's vocalization of Alegria's picado while he does palmas is the same speed his brain forces his fingers to move. If you can't say it, you can't really control it.
