I'm currently playing back MP3's with a 44k sample rate, that worked well when I was running in VGA mode but now that I've switched to PAL I need to lower the rate.
If you want to go exactly by the PAL-rates, I'd suggest you use 22030hz instead of 22050hz

I was actually thinking of converting some albums to 22khz/16bit/stereo adpcm-files, in which case they would be playable even on an plain A1200 with fastmem (or even A500 in mono).