My neighbour bought an mp3 player for his Harley & I told him I’d look for a cheap SD card. Will a faster card make a difference? I can see getting a faster card for a camera, but most (if not all) mp3 players use a buffer, so I think a 60x card for less than half of a 133x card would be fine. I think it would just take longer to copy the files to the card.
You are correct, a slower card will perform just the same for playback.
Even the slowest flash card is more than fast enough for mp3 playback.