With digital files, 'sound quality' is fixed: Either they are played back, or they're not.
Burning on slower speeds reduce the chances of errors. Faulty discs will not have lesser sound quality as long as they work, but the errors might cause glitches in the playback or even make the disc unplayable.
CD players might be good or less good at handling errors. A disc that won't play in one CDP might work with another player.