MP3 's play with 320kbit / s is not a problem because the following values are sufficient for it!
Write sticka: ~ 4.3 Mbytes / s
Write Stickb: ~ 4.2 Mbytes / s
Read sticka: ~ 17.9 MB / s
Read Stickb: ~ 16.8 MB / s
Until now, I can these sticks, area of the car HiFi with max. 4GB still well recommended. (ADDENDUM FOLLOWS)