Thanks, pts. I think you're entirely correct that pieces don't need to be "worked up to speed"- that once they are internalized and understood the speed simply emerges. In this instance I'm using the left hand alone as an exercise to do something I haven't tried technically before, so I'm experimenting with speeding it up while maintaining a new technique. At the same time I'm playing the piece much more slowly with both hands, working on dynamics, phrasing and so forth. I hope that eventually the two somewhat separate approaches will come together.
Also thank you, nyiregyhazi. If I understand you correctly, you're talking about the sort of stability that comes from the fingers comfortably supporting the weight of a relaxed arm, and using that weight rather than muscle to produce sound. That is how I have always tried (mostly unsuccessfully) to approach playing. It seems that at high speeds this causes tension for me, and almost cramping in the forearm, so I'm trying this different method. (I have a vague memory of my teacher introducing me to a similar technique around 1983- the last time I was studying.) As you say, true tapping can't work except for stacatto, but I think at high speeds the separation will vanish. I listened to Gould playing Opus 10 no. 2, and to my ear (not the most educated) that is what's going on. What I'm hoping is that eventually there will be a near continuum between weighted,stable playing and weightless rapid "tapping." I am already discovering that to keep the tapping even, I need to keep my forearm quite low, almost as if I WERE supporting the arm with the fingers. I hope I'm makng myself clear- and I apologize if I've misunderstood you.
Cheers, Sasha
pts, I meant to mention that my whole effort here is NOT to muscle through, even if that's possible. If i have any success I'll try 10 2; right now it seems beyond my reach. Thanks again.