No, there’s no recommended Class card for the Fuze+ or any of the Sansa players. Anything larger than a Class 2 though, in my opinion is a waste of money. The Class (or speed) rating of the card only pertains to the “writing to” the card, not the “reading from” it.
The faster cards are designed for use in cameras. While you may save a couple minutes in transfer time if you intend to load the card up completely in one fell swoop, you’d have to use a high-speed card reader see this time savings. If the card is in the player while you’re transferring the files, your transfer speed is limited by the reader circuitry inside the player.
My advice? Don’t waste your money on the faster cards if all you’re going to use them for is an mp3 player. 
