48k use to be better for sync with picture. I'm not sure that is true anymore. Things stay in sync now-a-days and that was just not possible without locking things together years ago.
As far as hearing the difference...You can hear the difference if you've been working a lot in one rate and then change. Say you work/mix a song for 8-10 hours and you now hear the song (assuming the speed is correct) in the other rate, it will sound different and most will notice it ever so slightly. If you are highly tuned in you can hear it, but not casually.