a secure card can accept encrypted data such as protected audio. All premium cards are sold based on their superior speed ratings. If the host and controller chips in partnering equipment can handle the speed transfers will be faster. For the KN a 133 speed is overkill and a complete waste of money, though you may notice a difference on pc transfer though you will be very hard pressed to actually find a card reader or host chip-set that fast, for read perhaps with the latest state of the art, but not for write so far.

File location is immaterial in my view. I have 256, 512 and 1G with the folder and playlist structure substantially filled. With alphabet, number load and playlists it is no different finding something compared to a 64 or 128 card filled with many hundreds of styles.