High speed is best for when you're writing to the card, such as when using it in a camera and it has to put the image on as quickly as possible, and then be ready for the next one. If you're just playing music, like we're doing, the unit is reading from the card, and having a high speed card doesn't make a difference. I tested high speed and regular speed SD cards using a tool on my Pocket PC, and when it comes to reading, sometimes the high speed cards were actually slower. Save $$ and stick with the regular speed for playing music.