Just picked it up again - clearly, a practicing version so far in other words.
How do you stay so free?
its a piece I like coming back to for shorter periods of time, but I wonder if I'll ever be able to play it satisfyingly up to tempo.
make sure 1-2 are relaxed all of the time
slowly...every day...make sure 1-2 are relaxed all of the time (if you take it too fast, they can get tense when they're not playing anything). When practicing slowly, I often play the upper voice mezzo forte or so.