I find turning off "show reference waveforms" can speed things up a little. But yes, it's frustrating how FCPX constantly has to rewrite the waveforms. It's quite similar to FCP7.
Also, hiding waveforms in the event library can help the timeline redraw quicker.
Premiere seems to have this one in the bag. Waveforms seem to be persistant through the timeline when scrolling. But I haven't used it enough to verify if it works with zooming in and out when playing (which X does not, unfortunately).
Michael Garber
5th Wall - a post production company