I found the information in the manual incomplete vs the plethora of options available and spent about 30mins on the phone with Pioneer to get the maximum class information.
Here's what you need to know:
Compatible physical format - Version 2.00
Max capacity memory - 8GB
File system - FAT16, FAT32
*NOT IN MANUAL*
Maximum Class 4: 4 MB/sec minimum data transfer rate
Hope this helps...